134 couES, 



lying the most laterally of any of them. It finishes by insertion, by 

 an aponeurosis of blended tendons, into the i-o lower cervical verte- 

 brae, at the apices of their transverse processes. 



A second lumbar plaife is thicker and narrower: like the last, it 

 arises from the apex of the ilium, and runs to the last rib ; it may 

 be a disintegration from the sacro-lumbalis ; but it seems to represent 

 lumbar continuation of a series of 'levatores costaram'? 



Quadratus lumborum. — This is rather thin, subtriangular, arising, 

 like the two last, from the iliac extremity and passing to the last 

 and next to the last, rib, with attachment also to vertebrae on its way. 



Thus there is no very remarkable deviation from a usual standard, 

 nor any specially interesting conformation of the cervico-dorsal ver- 

 tebral muscles. Among notable absentees, however, the serrati postici 

 may be mentioned. As a whole, the back muscles are not very large ; 

 those of the nape exceed them, comparatively; and these again are 

 surpassed in development and complexity of structure by the caudal 

 muscles destined to move the great heavy thick-skinned, fat-laden tail 

 that acts as a rudder when the animal is swimming. 

 d. Of the Tail. 



Levator caudtjz. — This is the uninterrupted prolongation of the lon- 

 gissimus to the tip of the tail. As the muscle passes dovm over the 

 back of the sacrum, it forms a single thick terete fleshy belly on either 

 side, filling the deep groove between the ilium and vertebral spines, 

 soon tapering and filling the similar groove on either side between 

 spinous and articular processes of caudal vertebrae, with attachments 

 all along its course. These last consist, on the upper part of the tail 

 at least, of distinct tendons terminating the muscular fasciculi that are 

 given off; they are implanted into zygapophyses. Towards the tip 

 of the tail, such definite arrangement is scarcely or not demonstrable. 



Extensor lateralis. — The median extensor of the tail is small com- 

 pared with this lateral one that forms the chief bulk of extending 

 muscle. The latter is incompletely divisible above into two portions ; 

 the larger one arises from the back of the iliac extremity ; the smaller 

 and more lateral portion lower down on the same bone ; the two are 

 afterward blended. The superior part mostly fills the fossa between 

 articular and transverse processes, lying upon the latter. Its upper 

 surface is invested with a strong dense fibrous sheath, that may be 

 split into numerous tendons, each of which arises from a partly dif- 

 ferentiated muscular fasciculus. Tendons thus extend to the tip 

 of the tail, but most of them pass a little obliquely inward towards 

 the median line for insertion, — an arrangement most obvious along the 

 middle of the tail. The lateral bundle of the muscle gives off from 

 its border and under surface about 6 distinct tendons from muscular 

 fasciculi, that pass to definite insertion into the tips of the transverse 



