484 University of California Publications in Geology [Vol.7 



pophyses are nowhere developed to the extent that they are in 

 the river otter, and the anapophyses are much reduced. The 

 anapophyses are present on the first lumbar vertebra, indicated 

 in the second, but practically obsolete in the third. The same 

 elements are indicated as rudiments even on the third, fourth 

 and fifth lumbar vertebrae in the mounted skeleton at Stanford 

 University. 



In Lutra the anapophyses are well developed on every lumbar 

 vertebra but the fifth and sixth. Posteriorly in the sea-otter the 

 metapophyses are reduced. The bodies or centra of all the verte- 

 brae are, as compared with those of the river otter, shorter antero- 

 posteriorly relatively to length of trunk, and relatively higher. 

 The zygapophysial facets are much reduced, and the epiphyses 

 are developed much more highly ; to such a degree, in fact, that 

 the heads of the anterior eleven pairs of ribs articulate, not on 

 the bodies of the vertebrae proper, but on the epiphyses between 

 them. 



There is apparently much greater flexibility in the vertebral 

 column of the sea-otter, the vertebrae being not nearly so firmly 

 locked together. The vertebrae show considerable resemblance to 

 those of the seal, in which the zygapophyses are much reduced, the 

 intervertebral foramina are large, there are no anapophyses, the 

 bodies of the vertebrae are short anteroposteriorly, the spinous 

 processes are very much reduced, and the epiphyses are prominent 

 (a similar though lesser tendency to have the anterior pairs of 

 ribs articulating on the epiphyses alone being apparent). 



Sacrum. — Zygapophyses are not noticeable upon the sacrum 

 of the sea-otter, while on the river otter they are indicated. The 

 transverse process on the posterior sacral is much reduced in 

 Latax. 



Chevron. — There is no chevron in the sea-otter. Its position is 

 indicated by two knobs diminishing gradually in size distally, first 

 appearing ventrally on the seventh caudal vertebra and disappear- 

 ing as such about the eighteenth. In the river otter the chevron 

 first appears on the fourth caudal, where it forms a complete or 

 nearly complete ring. It is definitely arched upon the next two 

 or three vertebrae, and then gives place to two knobs, gradually 

 diminishing in relative size toward the distal end of the tail. 



