1908.] ANATOMY OF A FROG. 19 



and pass directly upwards, or very nearly so, from the region of 

 the transverse process of the vertebra to the under surface of the 

 suprascapula. They really arise from the transverse process. The 

 third mnscle (text-fig. 7, A, t.sc.,]). 28) is long and slender, arising 

 from the tip of a transverse process and inserted lower down on the 

 scapula. In Breviceps the slender thii-d muscle {transverso-sccqndoe 

 tertius) is plain ; bvit there are only two of the broad dorsally 

 running portions, and one of these has been already referred to 

 as the retrahens scapulae. Moreover these muscles seem to me 

 to arise fi-om the surface of the longissimus, and not from 

 transverse processes. 



Coraco-hitmeralis. — When the posterior part of the portio 

 sternalis and the portio abdominalis of the pectoralis are cut 

 thi'ough and reflected, two muscles are brought into view without 

 any fui'ther dissection and when the Frog is lying upon, its back. 

 These are of unequal size, the smaller of the two lying nearest to 

 the coraco-humeral margin. I am disposed to regard this muscle 

 as corresponding to that which I have termed " pectoralis minor " 

 in Fipa and in Rana guppyi. It arises mainly from the coracoid, 

 but some of its fibres appear to reach the sternum. It is inserted 

 ■on the humerus to the posterior side of the insertion of the 

 pectoralis abdominalis, i. e., below that muscle as seen in the 

 position of dissection referred to. The larger muscle I term, 

 therefoi-e coraco-humeralis, which arises from the same bone and 

 cai-tilage as the last. Towards its insertion it is a much larger 

 muscle than the last described, and its insertion is farther down 

 the humerus, i. e., nearer to the hand. Both muscles are fleshy 

 throughout. 



§ 21'uscles of the Dorsal Surface. 



In Rana the muscles of the back are covered by, and also in 

 some cases arise from, the fascia dorsalis which is attached in the 

 middle line to the spinous processes of the vertebrae. In Rana 

 gup'pyi, where on account of the size of the frog this fascia is 

 specially thick, it has not obviously any more relations to the 

 depressor mandibulas than to the latissimus dorsi or the obliquus 

 externus, all of which aiise from it and are in perfect continuity 

 with it. It cannot be spoken of as the tendon of origin of any 

 one or indeed of all of these muscles. It is described by Ecker in 

 his ' Monograph of the Frog ' in a separate paragraph as something- 

 distinct from the ensuing muscles. It is to be assumed, however, 

 that in common with many other tendinous structures this fascia 

 dorsalis is to be referred to a previously existing sheet of muscle 

 But there is nothing in Rana to connect it definitely with any of 

 the muscles which arise from it, excepting perhaps the obliquus 

 externus on account of its larger size. It must be remembered, 

 however, that in Xenopus {Dactylethra) the latissimus dorsi is of 

 very large size *, and in shrinking to the dimensions which it 



* Manrer, "Die ventrale Rumpfmusknlatur der Aniiren Amphibien," Morph. 

 JB. 1895; and Beddard, P. Z. S. 1895, p. 846 (and footnote). 



9* 



