Cranial Structure of Varanus Komodoensis As Revealed by Computed-Tomographic Imaging

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Article Cranial Structure of Varanus komodoensis as Revealed by Computed-Tomographic Imaging

Sara Pérez 1, Mario Encinoso 2 , Juan Alberto Corbera 1 , Manuel Morales 1, Alberto Arencibia 3 , Eligia González-Rodríguez 1 , Soraya Déniz 2 , Carlos Melián 2, Alejandro Suárez-Bonnet 3 and José Raduan Jaber 3,*

1 Instituto Universitario de Investigaciones Biomedicas y Sanitarias (IUIBS), Facultad de Veterinaria, Universidad de Las Palmas de Gran Canaria, Trasmontaña, Arucas, 35413 Las Palmas, Spain; [email protected] (S.P.); [email protected] (J.A.C.); [email protected] (M.M.); [email protected] (E.G.-R.) 2 Hospital Clínico Veterinario, Facultad de Veterinaria, Universidad de Las Palmas de Gran Canaria, Trasmontaña, Arucas, 35413 Las Palmas, Spain; [email protected] (M.E.); [email protected] (S.D.); [email protected] (C.M.) 3 Departamento de Morfologia, Facultad de Veterinaria, Universidad de Las Palmas de Gran Canaria, Trasmontaña, Arucas, 35413 Las Palmas, Spain; [email protected] (A.A.); [email protected] (A.S.-B.) * Correspondence: [email protected]

Simple Summary: We investigated the head of Komodo dragons using CT imaging. Cross-sections show that all cranial bones can be delineated, while soft tissue structures are evident but not clearly Citation: Pérez, S.; Encinoso, M.; identifiable without an anatomical atlas. Additional three-dimensional reconstructed and maximum Corbera, J.A.; Morales, M.; Arencibia, intensity projection images of the head were presented to depict bony structures. The anatomical A.; González-Rodríguez, E.; Déniz, S.; structures identified on the CT images could help further assess the head of the Komodo dragon. Melián, C.; Suárez-Bonnet, A.; Jaber, J.R. Cranial Structure of Varanus Abstract: This study aimed to describe the anatomic features of the normal head of the Komodo komodoensis as Revealed by Computed-Tomographic Imaging. dragon (Varanus komodoensis) identified by computed tomography. CT images were obtained in Animals 2021, 11, 1078. https:// two dragons using a helical CT scanner. All sections were displayed with a bone and soft tissue doi.org/10.3390/ani11041078 windows setting. Head reconstructed, and maximum intensity projection images were obtained to enhance bony structures. After CT imaging, the images were compared with other studies and reptile Academic Editors: anatomy textbooks to facilitate the interpretation of the CT images. Anatomic details of the head Matilde Lombardero and Mar of the Komodo dragon were identified according to the CT density characteristics of the different Yllera Fernández organic tissues. This information is intended to be a useful initial anatomic reference in interpreting clinical CT imaging studies of the head and associated structures in live Komodo dragons. Received: 1 March 2021 Accepted: 7 April 2021 Keywords: computed tomography; head; Komodo dragon Published: 9 April 2021

Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in 1. Introduction published maps and institutional afﬁl- iations. The introduction of imaging diagnostic techniques has revolutionized the knowledge in reptile medicine. The radiographic evaluation has been traditionally used by clini- cians [1]. Nonetheless, the progressive increase in modern imaging modalities such as computed tomography (CT) and magnetic resonance imaging has improved diagnostic abilities in reptile medicine and research [2]. Therefore, these techniques represent an Copyright: © 2021 by the authors. Licensee MDPI, Basel, Switzerland. enormous resource that allows for fast, non-invasive anatomy visualizations of internal This article is an open access article structures that are challenging to interpret [2]. distributed under the terms and In recent years, the contributions of zoo veterinarians, researchers, and specialized conditions of the Creative Commons technicians (anatomists, radiologists, and wildlife and exotic specialists) working with Attribution (CC BY) license (https:// captive and free-ranging animals to prevent and treat diseases that threaten the survival creativecommons.org/licenses/by/ of species in wildlife conservation have increased [3]. Since 1996, the Komodo dragon 4.0/). (Varanus komodoensis) is listed as vulnerable by the Red List of the World Conservation

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Union [4]. To our knowledge, the anatomy of different species of reptiles has already been thoroughly described by radiology and CT [1,5–10], but only sparse numbers of these studies reported comprehensive descriptions of computed tomographic features of the head [1,5,6,9–12]. To date, not one of these reports investigates to what extent structures of the varanid head could be visualized and identiﬁed in low-resolution clinical CT-image data. In the Komodo dragon and other reptiles, the head conforms to a complex structure, which is challenging to interpret. The purpose of this study was to describe the normal anatomy of the head of the Varanus komodoensis by computed tomography, and three- dimensional head reconstructed images to assist in the understanding of the head and its associated structures.

2. Materials and Methods 2.1. Animals Two 17-year-old female specimens born in captivity at Reptilandia Park (Las Palmas, Spain) were imaged at the Veterinary Clinic Hospital of Las Palmas de Gran Canaria University. One female had a length of 225 cm (snout-vent length) and weighed 36 kg, whereas the other had a length of 190 cm and weighed 24 kg. No physical abnormalities were detected before the study. The Ethical Committee of Las Palmas de Gran Canaria University, College of Veterinary Medicine Section authorized the research protocol (MV- 2019/04). The owner of the animals was informed of the study and signed consent for participation in the study.

2.2. CT Technique Sequential transverse CT slices were obtained using a 16-slice helical CT scanner (Toshiba Astelion, Toshiba Medical System, Madrid, Spain). The animals were positioned symmetrically in ventral recumbency on the CT couch, and a standard clinical protocol (120 kVp, 80 mA, 512 × 512 acquisition matrix, 1809 × 858 field of view, a spiral pitch factor of 0.94, and a gantry rotation of 1.5 s) was used to acquire sequential transverse CT images of 1 mm thickness slice. The original transverse data were stored and transferred to the CT workstation. No CT density or anatomic variations were detected in the head of the dragons used in the study. In the CT technique, tissue density can be assessed directly on the image using the Hounsfield Unit scale, The range of values assumes 2000 shades of gray (between −1000 and +1000 HU). However, as the human eye cannot distinguish more than 30 shades, representing the entire range of values in an image implies not being able to visualize a large amount of information. Therefore, only a partial sector of the TC values previously selected by the operator (window selection) is represented by grayscale. Ultimately, the use of windows allows extracting the information that the computer has, showing only a part of it, which is of interest in each anatomical region. Therefore, bone window, soft tissue windows, brain window, and pulmonary window can be applied, delivering alternate streams of information. Thus, two CT windows were applied by adjusting the window widths (WW) and window levels (WL): a bone window setting (WW = 1500; WL = 300), and a soft tissue window setting (WW = 350; WL = 40). The original data were used to generate head volume-rendered reconstructed images after manual editing of the transverse CT images to remove soft tissues using a standard dicom 3D format (OsiriX MD, Geneva, Switzerland). In addition, maximum intensity projection (MIP) images were obtained to better display the outlines between bones and other lower- attenuation structures using an image viewer (OsiriX MD, Apple, Cupertino, CA, USA). MIP is a specific type of rendering in which the brightest voxel is projected into the 3D image. There tends to be much less variability in MIP image reconstruction than in volume rendering because fewer parameters are factored into the MIP algorithm [13]. Animals 2021, 11, 1078 3 of 12

3. Results 3.1. Transverse Computed Tomography Images Transverse sections are provided that demonstrate critical anatomical features of the varanid cranium (Figures1–6). Figure1 consists of three images: (C) Sagittal image of the head, where each line and number (I–VI) represents the approximate level of the following transverse CT images, (A) CT bone window, (B) CT soft tissue window. Figures2–6 represent transverse CT images where (A) CT bone window, and (B) CT soft tissue window. The CT images are presented in a cranial to caudal progression from the septomaxilla level (Figure1) to the brain stem level (Figure6). The comparison between available literature and CT images enabled us to identify most of the clinically relevant anatomic structures of the head. These features were identiﬁed according to location and the degree of attenuation of the different tissues. With regards to hard tissues, the CT images acquired using the bone window setting (Figures1–6A) provided good differentiation between the bones and the soft tissues of the head. Thus, the bones of the cranium (prefrontal, frontal, postorbital, parietal, squamosal, quadrate, jugal, pterygoid, basioccipital, parabasisphenoid, and maxilla), the mandible (dentary, angular, surangular, and articular bones) and hyoid bones were easily recog- nizable because of the high CT density in cortical bone and the low CT density in their medullary cavities. Most of these structures were also visualized with the soft tissue window setting (Figures1–6B). Air-ﬁlled structures, such as the nasal cavity, larynx, trachea, and the oral cavity gave negligible CT-tissue density and appeared black with both window settings. Soft-tissue structures—such as the jaw muscles, the labial and nasal glands, the eyes, and the Harderian glands—gave an intermediate CT density and appeared grey. The nervous structures (brain, cerebellum, lateral ventricles, brain stem, and spinal cord) were appreciated in both CT window modalities (Figures3–6). Animals 2021, 11, 1078 4 of 12 Animals 2021, 11, x FOR PEER REVIEW 4 of 12

Figure 1. Sagittal image of the head of Varanus komodoensis. The lines and numbers (I–VI) represent the approximate level Figure 1. Sagittal image of the head of Varanus komodoensis. The lines and numbers (I–VI) represent the approximate level of of the following transverse CT images (C). Transverse CT image of the head at the level of the nasal cavity corresponding the following transverse CT images (C). Transverse CT image of the head at the level of the nasal cavity corresponding to to line I. (A) CT bone window. (B) CT soft tissue window. These images are displayed so that the right side of the head is lineto the I. (viewer’sA) CT bone left window. and the (dorsalB) CT softview tissue is at window.the top. N: These Nasal images bone. are Sm: displayed Septomaxilla. so that Cnd: the right Dorsal side nasal of the conchae. head isto Cnv: the viewer’sVentral nasal left and conchae. the dorsal Prf: Prefrontal view is at bone. the top. 6. Maxillary N: Nasal bone. bone. Sm:T: Tooth. Septomaxilla. T’: Tooth. Cnd: Co: DorsalCavum nasal oris. conchae.Tg: Tongue. Cnv: Ms: Ventral Mus- nasalculus conchae.intermandibularis Prf: Prefrontal + Musculus bone. geniohyoideus 6. Maxillary bone. + Musculus T: Tooth. genioglossus. T’: Tooth. Co: D: Cavum Dentary oris. bone. Tg: Ig: Tongue. Infralabial Ms: glands. Musculus intermandibularis + Musculus geniohyoideus + Musculus genioglossus. D: Dentary bone. Ig: Infralabial glands.

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Figure 2. Transverse CT image of the head of Varanus komodoensis at the level of the nasal bone corresponding to line II. Figure 2. Transverse CT image of the head of Varanus komodoensis at the level of the nasal bone corresponding toline II. (A) CT bone window. (B) CT soft tissue window. These images are displayed so that the right side of the head is to the (A) CT bone window. (B) CT soft tissue window. These images are displayed so that the right side of the head is to the viewer’sFigure 2. left Transverse and the dorsalCT image view of is the at headthe top. of VaranusN: Nasal komodoensis bone. Prf: Prefrontat the levelal bone. of the Ns: nasal Nasal bone septum. corresponding Ng: Nasal to glands. line II. St:(viewer’sA )Stammteil, CT bone left andwindow. V: Vomer. the dorsal (B Sr:) CT viewSubconchal soft is tissue at the recess. window. top. N: Cht: Nasal These Choanal bone. imag tube. Prf:es are Prefrontal Nld: displayed Nasolacrimal bone. so Ns:that duct. Nasal the right Mx: septum. Maxillaryside Ng:of theNasal bone. head glands.T: is Tooth. to the St: Co:viewer’sStammteil, Cavum left V:oris. and Vomer. Tg:the dorsalTongue. Sr: Subconchal view Ms: is Musculus at recess.the top. Cht:intermandibula N: Nasal Choanal bone. tube.ris Prf: + Nld: MusculusPrefront Nasolacrimalal geniohyoideusbone. Ns: duct. Nasal Mx: + septum.Musculus Maxillary Ng: pterygoideus bone.Nasal T: glands. Tooth. + MusculusSt:Co: Stammteil, Cavum hyoglossus. oris. V: Vomer. Tg: Tongue.D: Sr:Dentary Subconchal Ms: bone. Musculus Mk.fs:recess. intermandibularis MeckeCht: Choanallian fossa. tube. Ig: + Nld: MusculusInfralabial Nasolacrimal geniohyoideusglands. duct.Fr: Frontal Mx: + MusculusMaxillary bone. bone. pterygoideus T: Tooth. + Co: Cavum oris. Tg: Tongue. Ms: Musculus intermandibularis + Musculus geniohyoideus + Musculus pterygoideus + Musculus hyoglossus. D: Dentary bone. Mk.fs: Meckelian fossa. Ig: Infralabial glands. Fr: Frontal bone. Musculus hyoglossus. D: Dentary bone. Mk.fs: Meckelian fossa. Ig: Infralabial glands. Fr: Frontal bone.

Figure 3. Transverse CT image of the head of Varanus komodoensis at the level of the eyes corresponding to line III. (A ) CT bone window. (B) CT soft tissue window. These images are displayed so that the right side of the head is to the viewer’s leftFigure and 3. the TransverseTransverse dorsal view CT isimage at the of top. the Frs:head Frontal of Varanus sinus. komodoensis Br: Brain. Sco:atat the the Scleral level level ofossicles. of the the eyes eyes Ls: cocorresponding Lens.rresponding Vh: Vitreous to to line line humor. III. III. ( (AA ))Hg: CT CT bone window. (B) CT soft tissue window. These images are displayed so that the right side of the head is to the viewer’s Harderianbone window. gland. (B )Sc: CT Sclera. soft tissue J: Jugal window. bone. Ec: These Ectopterygoid images are bone. displayed Pt: Pterygoid so that the bone. right D: side Dentary of the bone. head Mk.fs: is to the Meckelian viewer’s left and the dorsal view is at the top. Frs: Frontal sinus. Br: Brain. Sco: Scleral ossicles. Ls: Lens. Vh: Vitreous humor. Hg: fossa.left and mPt: the Musculus dorsal view pterygoideus. is at the top. Lxc: Frs: Laryngeal Frontal sinus. cavity. Br: Brain.Lxm: Laryngeal Sco: Scleral muscles. ossicles. Ms: Ls: Musculus Lens. Vh: intermandibularis Vitreous humor. Hg: + Harderian gland. Sc: Sclera. J: Jugal bone. Ec: Ectopterygoid bone. Pt: Pterygoid bone. D: Dentary bone. Mk.fs: Meckelian MusculusHarderian geniohyoideus gland. Sc: Sclera. + Musculus J: Jugal bone. genioglossus Ec: Ectopterygoid + Musculus bone. hy Pt:oglossus. Pterygoid Crc: bone. Cricoid D: Dentarycartilage. bone. Arc: Mk.fs:Arytenoid Meckelian cartilage.fossa. Co: mPt: Cavum Musculus oris. Sr:pterygoideus. Sublingual recess.Lxc: Laryngeal cavity. Lxm: Laryngeal muscles. Ms: Musculus intermandibularis + Musculusfossa. mPt: geniohyoideus Musculus pterygoideus. + Musculus Lxc: genioglossus Laryngeal + cavity. Musculus Lxm: hy Laryngealoglossus. muscles.Crc: Cricoid Ms: cartilage. Musculus Arc: intermandibularis Arytenoid carti- + lage.Musculus Co: Cavum geniohyoideus oris. Sr: Sublingual + Musculus recess. genioglossus + Musculus hyoglossus. Crc: Cricoid cartilage. Arc: Arytenoid cartilage. Co: Cavum oris. Sr: Sublingual recess.

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FigureFigure 4. Transverse CT imageimage ofof thethe headhead ofofVaranus Varanus komodoensis komodoensisat at the the level level of of the the parietal parietal bone bone corresponding corresponding to to line line IV. IV. (A) CT bone window. (B) CT soft tissue window. These images are displayed so that the right side of the head is to the Figure(A) CT 4. bone Transverse window. CT (B image) CT soft of the tissue head window. of Varanus These komodoensis images are at displayedthe level of so the that parietal the right bone side corresponding of the head is to to line the viewer’s left and the dorsal view is at the top. P: Parietal bone (frontoparietal suture). Pfr-Po: Postfrontal + Postorbital IV.viewer’s (A) CT left bone and window. the dorsal (B) viewCT soft is attissue the top.window. P: Parietal These boneimages (frontoparietal are displayed suture).so that the Pfr-Po: right Postfrontalside of the head + Postorbital is to the bone. Br: Brain. Sp: Sphenoid bone. Pt: Pterygoid bone. San: Surangular bone. Co: Coronoid bone. Co: Cavum oris. Tr: viewer’s left and the dorsal view is at the top. P: Parietal bone (frontoparietal suture). Pfr-Po: Postfrontal + Postorbital Trachea.bone. Br: Hs: Brain. Hyobranchial Sp: Sphenoid skeleton. bone. Ms: Pt: PterygoidMusculus intermandibularis bone. San: Surangular + Musculus bone. Co: geniohyoideus Coronoid bone. + Musculus Co: Cavum hyoglossus. oris. Tr: bone. Br: Brain. Sp: Sphenoid bone. Pt: Pterygoid bone. San: Surangular bone. Co: Coronoid bone. Co: Cavum oris. Tr: J:Trachea. Jugal bone. Hs: Hyobranchial Ig: Infralabial skeleton. glands. Ms:mAEM: Musculus Musculus intermandibularis adductor mandibulae + Musculus externus. geniohyoideus mPt-mAPM: + Musculus Musculus hyoglossus. ptery- Trachea. Hs: Hyobranchial skeleton. Ms: Musculus intermandibularis + Musculus geniohyoideus + Musculus hyoglossus. goideusJ: Jugal bone.+ Musculus Ig: Infralabial adductor glands. mandibularis mAEM: Musculusposterior. adductor mandibulae externus. mPt-mAPM: Musculus pterygoideus J: Jugal bone. Ig: Infralabial glands. mAEM: Musculus adductor mandibulae externus. mPt-mAPM: Musculus ptery- + Musculus adductor mandibularis posterior. goideus + Musculus adductor mandibularis posterior.

Figure 5. Transverse CT image of the head of Varanus komodoensis at the level of the postorbital + postfrontal bone corresponding to line V. (A) CT bone window. (B) CT soft tissue window. These images are displayed so that the right side of Figure 5. Transverse CT image of the head of Varanus komodoensis at the level of the postorbital + postfrontal bone corre- theFigure head 5. isTransverse to the viewer’s CT image left and of the headdorsal of viewVaranus is at komodoensisthe top. P: Parietalat the level bone. of Lv: the Lateral postorbital ventricle. + postfrontal Br: Brain. bone Ep: sponding to line V. (A) CT bone window. (B) CT soft tissue window. These images are displayed so that the right side of Epipterygoidcorresponding bone. to line Pt: V.Pterygoid (A) CT bonebone. window. Psp: Parabasisphenoid (B) CT soft tissue bone. window. Pfr-Po: post Thesefrontal images + postorbital are displayed bone. so San: that Surangu- the right the head is to the viewer’s left and the dorsal view is at the top. P: Parietal bone. Lv: Lateral ventricle. Br: Brain. Ep: larside bone. of the Co: head Cavum is to oris. the Tr: viewer’s Trachea. left Hs: and Hyobranchial the dorsal viewskeleton. is at Ms: the Musculus top. P: Parietal intermandibularis bone. Lv: Lateral+ Musculus ventricle. geniohy- Br: Epipterygoid bone. Pt: Pterygoid bone. Psp: Parabasisphenoid bone. Pfr-Po: postfrontal + postorbital bone. San: Surangu- oideus + Musculus hyoglossus. mAEM-mPSTs: Musculus adductor mandibulae externus + Musculus pseudotemporalis larBrain. bone. Ep: Co: Epipterygoid Cavum oris. bone.Tr: Trachea. Pt: Pterygoid Hs: Hyobranchial bone. Psp: skeleton. Parabasisphenoid Ms: Musculus bone. intermandibularis Pfr-Po: postfrontal + Musculus + postorbital geniohy- bone. superficialis. mLPt: Musculus levator pterygoideus. mPt: Musculus pterygoideus. oideusSan: Surangular + Musculus bone. hyoglossus. Co: Cavum mAEM-mPSTs: oris. Tr: Trachea. Musculus Hs: adductor Hyobranchial mandibulae skeleton. externus Ms: Musculus+ Musculus intermandibularis pseudotemporalis + superficialis.Musculus geniohyoideus mLPt: Musculus + Musculus levator pterygoideus. hyoglossus. mAEM-mPSTs: mPt: Musculus Musculuspterygoideus. adductor mandibulae externus + Musculus pseudotemporalis superﬁcialis. mLPt: Musculus levator pterygoideus. mPt: Musculus pterygoideus.

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Figure 6.Figure Transverse 6. Transverse CT image CT image of the of thehead head of of VaranusVaranus komodoensis at at the the level level of the of squamosalthe squamosal bone corrsponding bone corrsponding to line VI. to line VI. (A) CT(A )bone CT bone window. window. (B) ( BCT) CT soft soft tissue tissue window. window. TheseThese images images are are displayed displayed so that so that the right the right side of side the headof the is head to the is to the viewer’sviewer’s left and left the and dorsal the dorsal view view is isat atthe the top. top. Sq:Sq: SquamosalSquamosal bone. bone. P: Parietal P: Parietal bone. Cr:bone. Cerebellum Cr: Cerebellum (vermis). Bs: (vermis). Brain stem. Bs: Brain stem. Psp:Psp: Parabasisphenoid Parabasisphenoid bone.bone. Pt: Pt: Pterygoid Pterygoid bone. bone. San: San: Surangular Surangular bone. bone. Co: Cavum Co: Cavum oris. Tr: oris. Trachea. Tr: Hs:Trachea. Hyobranchial Hs: Hyobran- chial skeleton.skeleton. Ms: Ms: Musculus Musculus intermandibularis intermandibularis + Musculus + Musculu geniohyoideuss geniohyoideus + Musculus + hyoglossus.Musculus mAEM:hyoglossus. Musculus mAEM: adductor Musculus adductorexternus externus mandibularis. mandibularis. mPSTs-p: mPSTs-p: Musculus Musculus pseudotemporalis pseudotemp superﬁcialisoralis superficialis and profundus. and mPt: profundus. Musculus mPt: pterygoideus. Musculus pterygoideus. 3.2. Head Volume-Rendered Reconstructed Images 3.2. Head Volume-Rendered Reconstructed Images We provide images of the three-dimensional structure of the Varanus cranium in dorsalWe provide and ventral images view (Figuresof the three-dimensio7 and8, respectively)nal andstructure the left lateralof the view Varanus (Figure cranium9). in dorsalVolume-rendered and ventral view reconstructed (Figures CT7 and images 8, resp providedectively) good and visualization the left lateral of the view different (Figure 9). Volume-renderedbones that compose reconstructed the skull. Thus, CT theimages orbital prov borderided was good circumscribed visualization by the of lacrimal, the different bonesthe that prefrontal, compose and the the skull. jugal Thus, bones the (Figures orbita7 land border9). Moreover, was circumscribed the jugal bone by wasthe lacrimal, distinguishable from the ectopterygoid (Figure9). At the posterodorsal border of the orbit, the prefrontal,the fusion of and postorbital the jugal and bones postfrontal (Figures bones 7 and could 9). Moreover, be seen in the the lateral jugal andbone dorsal was distin- guishablereconstructed from the CT ectopterygoid images (Figures (Figure7 and9). 9). In ventralAt the view,posterodorsal the following border bones of of the the orbit, the fusionneurocranium of postorbital were and clearly postfrontal delineated: bones the parabasisphenoid, could be seen in the the basioccipital, lateral and and dorsal the recon- structedprootic CT (Figure images8). (Figures The junction 7 and between 9). In premaxilla ventral view, and maxilla the following with the tooth bones arranged of the neurocra- in niuma curvedwere clearly row was delineated: identiﬁed in thethe lateral parabasisp and ventralhenoid, view the (Figures basioccipital,8 and9). In theand lateral the prootic view, this tooth row curved with the margin of the mandible and maxillary. Besides, the (Figure 8). The junction between premaxilla and maxilla with the tooth arranged in a primary curvature of the maxilla was convex, whereas that of the mandible was concave. curvedIn addition, row was the identified coronoid processin the lateral was quite and prominent, ventral view and the (Figures surangular 8 and and 9). articular In the lateral view,bones this weretooth observed row curved extending with caudally the margin (Figure of9 ).the mandible and maxillary. Besides, the primary curvature of the maxilla was convex, whereas that of the mandible was concave. In addition, the coronoid process was quite prominent, and the surangular and articular bones were observed extending caudally (Figure 9).

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Figure 7. Three-dimensional volume-rendered reconstruction image of the cranium of Varanus komodoensis. Dorsal aspect. FigurePmx: 7. Three-dimensional Premaxillary bone. Mx: volume-rendered Maxillary bone.reconstruction Sm: Septomaxilla. image N: Nasal of the bone. cranium Prf: Prefrontal of Varanus bone. komodoensis Fr: Frontal . Dorsalbone. L: aspect. Pmx: PremaxillaryLacrimalFigure 7. bone.Three-dimensional bone.J: Jugal Mx: bone. Maxillary volume-renderedQ: Quadrate bone. bone. Sm: reco Sq: Septomaxilla.nstruction Squamosal. image Pfr-Po: N: of Nasal thePostfrontal cranium bone. Prf:+of postorbital. Varanus Prefrontal komodoensis P: bone.Parietal.. Fr:Dorsal Pro: Frontal Prootic. aspect. bone. L: LacrimalSan:Pmx: bone. Surangular Premaxillary J: Jugal bone. bone.bone. Cv1: Mx: Q: First QuadrateMax cervicalillary bone.vertebra. Sm: Sq: Cv2:Septomaxilla. Squamosal. Second cervical Pfr-Po:N: Nasal vertebra. Postfrontal bone. Prf: Prefrontal + postorbital. bone. P:Fr: Parietal.Frontal bone. Pro: L: Prootic. San: SurangularLacrimal bone. bone. J: Jugal Cv1: bone. First Q: cervical Quadrate vertebra. bone. Sq: Cv2: Squamosal. Second Pfr-Po: cervical Postfrontal vertebra. + postorbital. P: Parietal. Pro: Prootic. San: Surangular bone. Cv1: First cervical vertebra. Cv2: Second cervical vertebra.

Figure 8. Three-dimensional volume-rendered reconstruction image of the cranium of Varanus komodoensis. Ventral aspect. Mx: Maxillary bone. D: Dentary bone. San: Surangular bone. Art: Articular bone. Q: Quadrate bone. Bo. Basioccipital bone. Psp:Figure Parabasisphenoid 8. Three-dimensional bone. volume-rendered Pro: Prootic bone. reco Pt:nstruction Pterygoid image bone. of Pa: the Palatine cranium bone. of Varanus V: Vomer. komodoensis Sm: Septomaxilla.. Ventral aspect. N: Figure 8. Three-dimensional volume-rendered reconstruction image of the cranium of Varanus komodoensis. Ventral aspect. NasalMx: Maxillary bone. Fr: bone. Frontal D: Dentarybone. P: Parietalbone. San: bone. Surangular Ha: Hyoid bone. apparatus. Art: Articular Cv2: Second bone. Q: cervical Quadrate vertebra. bone. Bo. Basioccipital bone. Mx: MaxillaryPsp: Parabasisphenoid bone. D: Dentary bone. bone. Pro: Prootic San: Surangular bone. Pt: Pterygoid bone. Art: bone. Articular Pa: Palatine bone. bone. Q: Quadrate V: Vomer. bone. Sm: Bo.Septomaxilla. Basioccipital N: bone. Psp: ParabasisphenoidNasal bone. Fr: Frontal bone. bone. Pro: P: Parietal Prootic bone. bone. Ha: Pt: Hyoid Pterygoid apparatus. bone. Cv2: Pa: Second Palatine cervical bone. vertebra. V: Vomer. Sm: Septomaxilla. N: Nasal bone. Fr: Frontal bone. P: Parietal bone. Ha: Hyoid apparatus. Cv2: Second cervical vertebra.

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Figure 9. Three-dimensionalFigure 9. Three-dimensional volume-rendered volume-rendered reco reconstructionnstruction imageimage of of the the cranium cranium of Varanus of Varanus komodoensis komodoensis. Lateral aspect.. Lateral aspect. Pmx: PremaxillaryPmx: Premaxillary bone. Mx: bone. Max Mx:illary Maxillary bone. bone. Prf: Prf: Prefrontal Prefrontal bone. N: N: Nasal Nasal bone. bo Fr:ne. Frontal Fr: Frontal bone. L: bone. Lacrimal L: bone. Lacrimal J: bone. J: Jugal bone. JugalEc: Ectopterygoid bone. Ec: Ectopterygoid bone. bone.Pt: Pterygoid Pt: Pterygoid bone. bone. Ep: Ep: Epipterygoid.Epipterygoid. Q: QuadrateQ: Quadrate bone. Sq: bone. Squamosal. Sq: Squamosal. Pfr-Po: Pfr-Po: Postfrontal +Postfrontal postorbital. + postorbital. Pro: Prootic. Pro: Prootic. D: Dentary D: Dentary bone. bone. T: T: Tooth. Tooth. San: San: Surangular Surangular bone. bone. Art: Articular Art: Articular bone. Co: Coronoidbone. Co: Coronoid bone. Ha: Hyoidbone. Ha:apparatus. Hyoid apparatus.

3.3. Maximum Intensity Projection (MIP) Images 3.3. Maximum Intensity Projection (MIP) Images Two MIP images corresponding to dorsal (Figure 10) and ventral (Figure 11) views of Twothe varanid MIP images skull were corresponding selected. These imagesto dorsal were (Figure able to resolve 10) and the relationventral between (Figure 11) views of the thevaranid bones thatskull comprise were theselected. head. The These dorsal images MIP image were showed able the to junctionresolve between the relation the between premaxilla and the maxilla. We were also able to show how the laminar disposition of the the bonesvomer that supports comprise the septomaxilla the head. (Figure The dorsal10). This MIP last finding image could showed be better the distinguished junction between the premaxillain the ventraland the MIP maxilla. image (Figure We were11). The also relation able between to show the how lacrimal, the the laminar prefrontal, disposition and of the vomerthe supports frontal bones the was septomaxilla seen in the dorsal (Figure view (Figure10). This 10). Atlast the finding posterodorsal could border be ofbetter distin- guishedthe in orbit, the the ventral fusion ofMIP postorbital image and (Figure postfrontal 11). bonesThe relation could be easilybetween seen. the In addition lacrimal, the pre- to these observations, the junction of the frontal and the parietal bones were identified in frontal,dorsal and (Figurethe frontal 10) and bones ventral was (Figure seen 11 in) MIP the images.dorsal Theview ventral (Figure MIP 10). image At showed the posterodorsal borderexcellent of the visualizationorbit, the fusion of the pterygoid, of postorbital a flat, Y-shaped and postfrontal bone. This bone bones provides could a rounded be easily seen. In additionprocess to these that contacts observations, the caudal the border junction of the palatine.of the frontal Moreover, and this the view parietal displayed bones the were identified injunction dorsal between (Figure the parabasisphenoid,10) and ventral the (Figure prootic, and11) theMIP basioccipital images. bones.The ventral This last MIP image bone forms the ventral portion of the occipital condyle. showed excellent visualization of the pterygoid, a flat, Y-shaped bone. This bone provides a rounded process that contacts the caudal border of the palatine. Moreover, this view displayed the junction between the parabasisphenoid, the prootic, and the basioccipital bones. This last bone forms the ventral portion of the occipital condyle.

Animals 2021, 11, 1078 10 of 12 Animals 2021, 11, x FOR PEER REVIEW 10 of 12

Animals 2021, 11, x FOR PEER REVIEW 10 of 12

Figure 10. Dorsal MIP image of the cranium of Varanus komodoensis. Px: Premaxillary bone. Mx: Maxillary bone. Sm: Sep- Figure 10. Dorsal MIP image of the cranium of Varanus komodoensis. Px: Premaxillary bone. Mx: Maxillary bone. Sm: tomaxilla. V: Vomer. N: Nasal bone. Prf: Prefrontal bone. Fr: Frontal bone. L: Lacrimal bone. Sco: Scleral ossicles. J: Jugal Septomaxilla. V: Vomer. N: Nasal bone. Prf: Prefrontal bone. Fr: Frontal bone. L: Lacrimal bone. Sco: Scleral ossicles. J: bone.Figure Pfr-Po: 10. Dorsal Postfrontal MIP image + postorbital. of the cranium P: Parietal. of Varanus So: Suprao komodoensisccipital.. Px: Sq: Premaxillary Squamosal. Ost: bone. Osteoderms. Mx: Maxillary Cv1: bone. First Sm: cervical Sep- Jugalvertebra.tomaxilla. bone. Cv2: Pfr-Po: V: Vomer. Second Postfrontal N: cervical Nasal + vertebra.bone. postorbital. Prf: Prefrontal P: Parietal. bone. So: Fr: Supraoccipital.Frontal bone. L: Sq:Lacrimal Squamosal. bone. Sco: Ost: Scleral Osteoderms. ossicles. Cv1:J: Jugal First cervicalbone. vertebra.Pfr-Po: Postfrontal Cv2: Second + postorbital. cervical vertebra. P: Parietal. So: Supraoccipital. Sq: Squamosal. Ost: Osteoderms. Cv1: First cervical vertebra. Cv2: Second cervical vertebra.

Figure 11. Ventral MIP image of the cranium of Varanus komodoensis. D: Dentary bone. Mx: Maxillary bone. San: Surangular bone. Art: Articular bone. Bo. Basioccipital bone. Psp: Parabasisphenoid bone. Oc: Occipital condyle. Pro: Prootic bone. Figure 11. Ventral MIP image of the cranium of Varanus komodoensis. D: Dentary bone. Mx: Maxillary bone. San: Surangular FigureSm: Septomaxilla. 11. Ventral MIP V: imageVomer. of Pa: the Palatine cranium bone. of Varanus Pt: Pterygoid komodoensis bone.. Cv1: D: Dentary First cervical bone. verteb Mx: Maxillaryra. Cv2: Second bone. San: cervical Surangular ver- bone. Art: Articular bone. Bo. Basioccipital bone. Psp: Parabasisphenoid bone. Oc: Occipital condyle. Pro: Prootic bone. bone.tebra. Art: Articular bone. Bo. Basioccipital bone. Psp: Parabasisphenoid bone. Oc: Occipital condyle. Pro: Prootic bone. Sm: Sm: Septomaxilla. V: Vomer. Pa: Palatine bone. Pt: Pterygoid bone. Cv1: First cervical vertebra. Cv2: Second cervical ver- Septomaxilla.tebra. V: Vomer. Pa: Palatine bone. Pt: Pterygoid bone. Cv1: First cervical vertebra. Cv2: Second cervical vertebra.

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4. Discussion In recent years, the contribution of imaging techniques to reptile medicine has increased the knowledge in veterinary practice and research [4–6,12]. Traditionally, radiography and ultrasonography have been used to obtain information on the bony and the main soft-tissue structures of different reptile regions [14,15]. More advanced imaging techniques, such as computed tomography, have become increasingly common in veterinary clinical practice [15]. Third and fourth generation CT scanners give considerable advantages over traditional radiography: body sections from different tomographic planes, fair anatomic resolution without superimposition of the tissues, and a higher differentiation of tissue densities allow better detection of several diseases [6,15,16]. Nonetheless, its use in reptile medicine is still limited because of the cost of the equipment, availability, and logistic problems of acquiring CT images in these animals [6,15]. The cranium of the genus Varanus is a complex structure that has received some attention in morphofunctional studies [12,17], perhaps due to the enormous disparity in the form that evolved among varanid lizards [18]. The head of this iconic varanid represents a complex structure, composed of various tissues with varying degrees of attenuation in radiographic images, making it a challenging object to assess. The two window settings used in our CT study facilitated the identification of the main head structures such as the bones of the skull, mandible, muscles, air-filled structures of the respiratory and digestive system, the nervousranium and other associated structures. Visualizing images through use of the “bone window” provided good resolution for skeletal structures, whereas the “soft tissue window” allowed us to distinguish the eyes and the nervous structures from the remaining soft tissues. Similar results were described in other studies conducted in reptiles [1,5,6,15]. Several causes have been reported to explain the low resolution of soft tissue structures showed in our study [1,15], such as the small volume of these species, the impossibility of reducing the field of view of the CT scanner, and the presence of bones embedded within the skin. These bones, called cephalic osteoderms, vary in shape and complexity and serve primarily as a defensive anatomical system to protect individuals during aggressive confrontations with other specimens [11]. To avoid this low resolution, some investigations reported the use of micro-CT scanners [17], although this equipment is not usually available in veterinary clinics [15]. Employing computed tomography, we were able to fully visualize the cranium in virtual reconstructions and MIP images. Thus, the reconstructed images showed a broad, dorsoventrally compressed cranium. The mandible was curved, and teeth were laterally compressed. This morphology contrasts with most other varanids, which feature a rela- tively narrow rostrum, a dorsoventrally tall cranium, and a straight ventral margin of the maxilla [18]. Additionally, an enormous variation of the orbit was observed, especially along the posterior margin of the orbit, which is closed in lizards, or semiclosed in these varanids. This fact is determined by variation in the shape, size, and presence of the jugal bone and variations in the postorbital and postfrontal bones [19]. MIP images proved a helpful tool in delineating bones in volume-rendered images. In conclusion, the CT images obtained in this study provided an adequate anatomical interpretation of the head of Varanus komodoensis. This information could be used to diagnose disorders involving the head of lizards, such as abscesses, metabolic bone diseases, fractures, and neoplasia.

Author Contributions: Conceptualization, A.A., S.P. and J.R.J.; Methodology, S.P., J.A.C., E.G.-R., A.S.-B. and M.E.; Formal analysis, J.R.J., M.E. and A.A.; Investigation, S.D. and M.M.; Writing— original draft, A.A. and J.R.J.; Writing—review and editing, C.M.; Supervision, J.R.J. All authors have read and agreed to the published version of the manuscript. Funding: This research received no external funding and the University of Las Palmas de Gran Canaria funded the study. Animals 2021, 11, 1078 12 of 12

Institutional Review Board Statement: The study was conducted according to the guidelines of the Declaration of Helsinki, and approved by the Ethical Committee of Las Palmas de Gran Canaria University, College of Veterinary Medicine Section (protocol code MV-2019/04). Data Availability Statement: Not applicable. Acknowledgments: In loving memory of Alvaro Domingo Rodriguez Garcia. We also thank Marisa Mohamad for her support and constructive comments. Conﬂicts of Interest: The authors declare no conﬂict of interest.

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