152 DE. J. MUEIE ON THE FOEM AKD STEUCTUEE OF THE MANATEE. 



From the extraordinary thickness of these respiratory muscles it would follow that 

 they possessed equal increment of power on the movements of the chest and belly. 

 This quality undoubtedly belongs to them ; but their contractive efforts must in a great 

 measure depend on the coordinate action of the remarkably placed diaphragm and the 

 potent thoracico-abdominal muscles. The ribs are each and all firmly fixed at their 

 vertebral ends, although comparatively free abdominally. 



The scalene muscle bounds and is closely adherent to the inner and median side of 

 the serratus magnus. It is a long, strong, fleshy slip, more than an inch broad, and has 

 origin at and partially covers the three anterior ribs from their angles inwards. In the 

 neck it passes along the tips of the transverse processes of the cervical vertebrse, and 

 is inserted into all but that of the atlas. 



Although described as single, there appears to be an imperfect division into an 

 anticus and posticus. The attachments of the inner and smaller portion are the trans- 

 verse processes of the three posterior cervical vertebree and the first rib. The outer, 

 broader and stronger portion has three cei-vical tendons — namely, two large and an 

 intervening very diminutive one. The anterior large and small tendons, separated by 

 the third cervical nerve, are attached to the outstanding process of the axis ; the 

 posterior large tendon is fixed to the succeeding vertebra. The latter portion of the 

 scalenus in question arises from the second and third ribs and interspaces. 



The rudimentary tiny slip of tendon referred to above, as being inserted into the axis 

 alongside but rather behind the first tendon, is not without interest. Its presence 

 demonstrates that the regular number of tendons exists in spite of the remarkable 

 deficiency of a cervical vertebra, compared with what obtains in other mammals. The 

 inferences derived therefrom have been discussed n connexion with the bones of the 

 neck. 



A vascular plexus of considerable extent intervenes between the scalene tendons and 

 the cervical plexus of nerves at their issue from the vertebral foramina. 



Eapp' says that the scalenus is wanting in the Manatee — a statement quite at variance 

 with my dissection. He admits its presence in the Porpoise ; so does Stannius^ who 

 names both a scalenus anticus and posticus to the first and second ribs. This agrees 

 with what Macalister^ and I have found in the Pilot "SVhale; but Carte* and he only 

 mention a single scalene in Balwnoptera rostrata. The relations of the nerves and 

 cervical vascular plexus in the Cete bear much resemblance to those of Sirenia. 



There appears to be a double scalenus in the Elephant^ — the superficial one, answer- 

 ing to the serratus anticus, being fleshy, of great size, and spreading upon the chest by 

 digitations as low as the fifth rib. 



So far as strength and action are concerned, the supei-ficial throat-portion of the 

 panniculus replaces the sterno-mastoid in the Manatee ; but the latter muscle, notwith- 



' ' Cetacea,' already quoted, p. 86. ' Loc. cit. p. 36 ; and Meckel, vol. vi. p. 156. 



• P. Z. S. 1867, p. 481. " PhU. Trans. 1868, p. 219. * Myologie, pis. 276 and 287. 6, 6'. 



