442 DR. J. MURIE ON THE ANATOMY OF THE WALRUS. 
the humerus. This powerful retractor of the limb is evidently that which Meckel’ 
doubtfully regards as a pectoralis minor. Cuvier considers the pectoralis minor to be 
absent in Carnivora; but in his and Laurillard’s ‘ Planches de Myologie’ the following 
divisions of the pectorales are designated and lettered*:—j, grand pectoral, portion 
sternale (sterno-humérien) ; j’, portion costale et méme ventrale; ?, portion profonde 
dite moyen ou petit pectoral. In their illustrations of Ursus americanus and Canis 
familiaris, subdivisions of the two latter are specially marked, as well as another 
presently to be described. The said segmentation of the pectoralis doubtless corre- 
sponds to the variations and abnormalities found in Man by numerous anatomists; more 
particularly, however, of late have they been referred to by Messrs. Wood* and 
Macalister. 
A third, very much smaller, narrow thoracic strip of muscle, which may be men- 
tioned in connexion with the pectoralis, is one which is found in the Otary, Seal, and 
other animals, as well as the Morse. It has origin from the manubrium or preesternum, 
and, passing band-like at nearly right angles outwards to the humerus, is fixed in front 
and to the outer ridge of the bicipital groove. 
To interpret the homology of this muscle, 1 may at once refer to the very ably 
reasoned paper of Professor Rolleston in the ‘ Linnean Transactions,’ 1868*, and to 
the various memoirs therein quoted. According to his reading I presume it would 
represent a subclavius, otherwise absent in the Morse. That it is the homologue of 
the so-called sterno-scapular muscle present in several Ungulata, Rodentia, and Car- 
nivora there is less room for doubt, though having a humeral insertion, which is not 
uncommon. Whilst I agree with Rolleston as to the close and often obvious connexion 
of the pectoralis major and minor (in this respect opposed to Pagenstecher’s views’), 
and also that the pectoralis secundus or levator humeri of birds is not an altered or 
derivative pectoralis minor, I am not so clearly convinced of the identity of the sterno- 
scapular and subclavius muscles. Unless these two are perfectly identical, it is probable 
that the epicoraco-humeral of Mivart® may be the homologue of the former of these 
two, and not necessarily the latter. With these remarks, it is not my intention at 
present further to discuss the moot points so ably sustained in the Oxford professor's 
paper. 
What I have described in Otaria jubata as the first part of the deltoid muscle is 
identical in Trichechus rosmarus (woodcut, fig. 3, D'); but there is no slip joining the 
supinator longus; these two muscles, however, are united very closely by fascia on the 
Anat. Comp. vol. yi. p. 251. * Vide Liste des Muscles. 
In his papers, Proc. Roy. Soc. 1865-68. 
On the “ Homologies of certain Muscles connected with the Shoulder-joint,” vol. xxvi. pt. 3. p. 609. 
® For which consult ‘ Der Zoologische Garten,’ 1867, and Rolleston, /. s. c. 
“On some points in the Anatomy of Echidna hystrix,’ Trans. Linn. Soc. vol. xxv. p. 383; and P. Z.8, 1867, 
p- 778, ‘ Myology of Iguana tuberculata.” 
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