Okajimas Fol. anat. jap., 48: 103-137, 1971 The M. Transversus Thoracis in Man and Monkey By Jun-ichiro Satoh Department of Anatomy, Faculty of Medicine, Nagasaki University, Nagasaki, Japan Received for publication, December 2, 1970— Of the Mm. thoracis proprii and profundi in man, the muscles that run across the ribs in the most inner layer of the thoracic wall have been termed the Mm. subcostales by Eisler. Of these, the group of muscles located in the mid-anterior chest are the Mm. transversi thoracis while those in the posterior chest are the Mm. subcostales in the narrow sense. The purpose of the present report is to describe the M. transversus thoracis in man and monkey, especially the nerve supply to these muscles which has not yet been documented in detail. The material of study consisted of bodies of adult Japanese (24 cases), Crab-eating monkey (Macaca irus, 15 cases) and Formosan mon- key (Macaca cyclopis, 15 cases). The condition on both sides of the body was examined with magnifying lenses having an illumination attach- ment. Findings I. Mm. transversi thoracis in man In man, the Mm. transversi thoracis were found to be flat, narrow muscles which are multiform being quite variable in shape. In the region of the lateral edge of the sternum, especially at the xiphoid process, they were united each other so that the muscles particularly the lower ones, frequently form so-called muscular digitation, the tip being the attachment to the rib (figures 1 and 2). 1. This muscle arose by tendon from the rib in the area of the costo- chondral joint, that is, from the region extending from the lateral tip of the costal cartilage to the bony rib. The insertion was the lateral edge of the sternum and xiphoid process, but the condition of the muscle at the attachment was somewhat variable by site with a higher mixture of tendinous fibers for the upper muscles while the insertion was mostly muscular for the lowest muscle which attached to the xiphoid process. Thus the lowest digitation was adjacent to the M. transversus abdominis. 103 104 Juniichiro Satoh Fig. 1. M. transversus thoracis in man (No. 524, (posterior aspect). (The muscles attached to the inner surface of the sternum) 2. In addition to the usual condition where the origin is from the area of the costochondral joint with insertion into the sternum or xiphoid process, close examination revealed instances in which the muscle arose from the intercostal space and terminated into the sternum or xiphoid process, and others in which the muscle arose from near the costo- chondral joint and inserted into the area adjacent to the sternocostal joint or into the rib or costal cartilage (table 1, 2, 3). 3. The Mm. transversi thoracis were located in a zone lying between the costochondral joint and the sternum. They never extended lateral- ly (distally) beyond this area. Moreover, this is the region where the M. intercostalis internus (Eisler) ends and where the M. intercostalis intermedius (Eisler) becomes exposed as a thick muscle layer beneath the pleura together with the N. intercostalis. Thus, the position of this muscle appears to supplement the area where the M. intercostalis internus is not present. The M. Transversus Thoracis in Man and Monkey 05 Fig. 2. M. transversus thoracis in man (No. 758, (posterior aspect). 4. This muscle ran medio-downward from its costal origin to its inser- tion, but the angle of this muscle to the sternum was the least for the upper muscles and increasingly greater for the lower muscle.until it is almost horizontal. 5. The origin of the first muscle was sometimes as high as the first rib and the last muscle may be from the seventh rib, but such cases Table 1. Relation between the origin and insertion in man. 106 Jun-ichiro Satoh 麺 鎖 哨 ・陰 鞠噌 磁 コ 屡 り 姻 。 ・瞭 縄 } 』 。 }. 嘱 ` 至 』 ご 。 。 』 ε 婁 臥 患 一 α 。 α ; 。 5 ω ε } …曜 ω 噌 1 . 〉 § の ( 勧 ω Φ 馨 順 ζ 睦 o 麟 嘩 弱 ノ 』 } 馨 巴 o 。 塵 ー 姦 匪 9 賃 。 匪 鞠 咽 1 の 。 8 ー づ 騨 ー ε 匹 gゆ の 』 爆 o α の駆 婁 ー > 巨 。 の ` こ ｢』 自 I 邸 の I お 。 ・陰 彦 捻 】. 。 お ≧ 轟 ξ ¢ の ① の 2 幽 』 き ρ 。 の こ } ・6 奮 o 』 ー 。 ε き 。, 。 ⇔緯 結 腹 ¢ ` 三 o 邸 9酢 o § ℃ ` £. 器 9 転 $ の で ε 邸 ・5 娼 ω 邸 ー 。 州 o 一 娼 お " 煽 濤 』 。 轟 唄 。 ね◎ 三 ε の 睾、 勧 も もo の 唄 ε 2 。 お 董 二 。 § 。 } ぐ・ 2同 。 糞蝋 篶 』 巴 ↑ 繍 身 . 畷 。 い ε 賃 。 ξ 占 " 婁 TbeM.Tr瓠sver8usThoracisi簸M鋤a擁dMonkey107 . 諺ω ℃ 。刷 琶 舞 8. 峯 .、 襲 臨 蓉. 霞. 妻 ヨ州 £ 聾 き の ・, 。 ぞ .。 の" ・, 濃 。. ℃ § § の 8 慧 。』 覇 鷲 石 日 。, ξ 慧州 き 巴 壱 ω … の 湯 二 お 。. お 霧 賃 費 8 ・ 9 6. 芝。 婁 5、 こ 蓄哨 。 ω 書。, 忘 必 - 三 結 嘗 綱 8 。 零 。 ヨ 賃 。 。の 綴 § ↑ も 燭。 £ £ … 嚥 濡 × ↑ 藁 ω. 燕 ×. 心 の・ 亡 ㌣. 。 8鴨 8 tO8tJun・ichiroSatoh ℃. の コ 信 咽 ρ 轟 O O 0う、 Q ρ一 6δ [自 The M. Transversus Thoracis in Man and Monkey 109 . ℃ O コ " θ哨 爆 O O ◎う. 〇 訟一 煽 ↑ 110 Jun-ichiro Satoh . ℃ O ゴ ¢ 掴 ρ q O O σ◎. 〇 一 ゆ 網 ↑ The M. Transversus Thoracis in Man and Monkey 111 . で O づ q 姻 騨 ¢ O O ひう. 〇 一 〇 65 臼 い 112 Jun-ichiro Satoh were very infrequent. Usually, these muscles arose from the second to sixth ribs (table 2). 6. In addition to cases where the muscle arose from the rib as a single muscle and inserted as a single muscle, there were instances in which the insertion was separated into two parts (figure 3, A-3, D). Converse- ly, two muscles arising from the same rib may unite to insert as a single muscle (figure 3, A-2). Moreover, the insertion of the muscles into the upper part of the sternum was by a single muscle or there may be a single union of two muscles. The insertion of the lower muscles, however, particularly the muscles from the lower ribs which insert into the xiphoid process, were located more adjacent to each other with overlapping in some areas so as to occasionally present an appearance similar to a single muscle sheet. Of course, there were instances in which a space remained be- tween adjacent muscles so that a complete muscle sheet was not formed. In contrast, at the origin these muscles were separated from each other so that they form muscular digitation which run lateralward to their site of origin from the rib. The number of muscular digitation varied, of course, depending upon the number of muscles that arose from the ribs, but there usually were five to six on each side of the body (table 3). Furthermore, the muscular digitations on each side of the body were not necessarily equal in number nor symmetrical in position. 7. The relation of this muscle to the intercostal space between its origin to insertion could be clearly determined for the muscles in the upper region but not for those in the lower region, particularly the muscle to the xiphoid process. The longer ones occupied three intercostal spaces while the shorter muscles may end in one intercostal space, but the majority occupied two intercostal spaces. 8. As mentioned above, close examination revealed that the sites of origin and insertion were variable. From the relation between the origin and insertion, it was possible to classify the muscle into four types (tables 3 and 4, figure 3). Type A: The origin is from an area extending from the lateral tip of the costal cartilage to the bony rib, in other words, the region of the costochondral joint, and the insertion is the sternum or xiphoid process. Type B: The origin is from the intercostal space with termi- nation into the sternum or xiphoid process. The M. Transversus Thoracis in Man and Monkey 113 . ぢ( 巴 の 煽 お ℃ $ 。ゆ a ) q. 舞 ε ・ §姻 § の 婁 霧 煽 碧 薯。 。舶 ・ 。 参 の ぎ 竃 〉 。・・ む。・ 角咽 114 Jun-ichiro Satoh Type C: Origin is from the rib and insertion is into the rib or costal cartilage. Type D: The muscle arises from the rib and separates into two, parts, one inserts into the sternum or xiphoid process while the other into the rib. This can be considered to be a mixture of types A and C. Of these various types, the most common was type A. When ex- amined by the rib of origin, types C and D tended to be comparatively more frequent among the upper muscles. Table 4. Types of M. transversus thoracis in man observed from the sites of origin and insertion. A muscle of type A most frequently had a single origin and a single insertion (type A-1). Other conditions seen in a few instances included the following : the muscle arose from the rib in two separate parts and united to insert as a single muscle (type A-2) the muscle was in one part at the origin but separated into two parts at the inser tion (type A-3) and the muscle was separated into two parts at both the origin and the insertion (type A-4). The last type A-4 may be considered to be the presence of two parallel type A-1 muscles from one rib (tables 3 and 4).