MAMMALIA. 
35 
1. The atlas coale,scecl with the other cervical vertohroe into one moss. 
a. The lateral processes of the atlas conical. Bnlcena. 
b. The lateral processes of the atlas rather broad, rounded, shorter 
below. Eubalmna. 
2. The atlas free from, and separate from, the other cervical yertebrse. 
Macleayius. 
B. The lateral process of the atlas and other cervical vertebrm on the 
lower pait of the side of the body. Hyperodon and Layenocetus. 
II. The neural arch low, scarcely raised, keeled on the upper edge ; the 
lateral processes very wide, occupying nearly the whole side-edge of tlie body 
of the vertebree. Atlas separate, free. Catodoniidee. 
Tlie paper is illustrated by figures of the cervical vertebree of the new 
species, of Catodon australis, and of Layenocetus latifrons. 
^Mr. Flower has made important communications on the 
skeletons of Whales in the Butch and .Belgian collections, Proc. 
Zool. Soc. I8GI, p. 384. He commences his memoir wdth 
general observations on the method to be followed in the exami- 
nation of skeletons of Cetaceans. The alterations, he says, 
which take place in the bones at different periods of life^ render 
it an object of primary importance to ascertain as near as may 
be, the relative age of the individual under examination. He 
distinguishes three stages of growth : — I. Very young and young 
stage : all the epiphyses of the vertebral column, and of both 
ends of the humerus, radius, and ulna are still separate, and the 
processes of the yertebrse are obviously unfinished, abruptly and 
roughly truncated. The animal remains in this condition until 
it has attained to more than half the length of the adult. 
II. Adolescent stage : both epiphyses of the humerus, those of 
the upper end of the radius and ulna, and those of the bodies of 
the anterior cervical and the posterior caudal vertebrae are united, 
while those of the greater part of the column are still free. 
III. Adult stage \ all the vertebral epiphyses arc anchylosed. 
The obliteration of the sutures of the cranium affords com- 
paratively much less indication as to age, the majority of the 
bones remaining distinct throughout life. 
The author then shows that the amount of variation found 
among different individuals of the same species is much less than 
was formerly supposed, as long as many species were thrown 
together into one. As regards size, the adult animals of Balcena 
mysticetus have a tolerably limited range of variation within ifc 
few feet of either side of 55' : Balmnoptera rostrata does not 
appear to exceed 31'; Megaptera longimana between 45' and 50'; 
Physalus antiquorum between 60' and 70'. There is scarcely 
any variation in the number of vertebrse and ribs, provided the 
skeleton is complete ; Balamoptera rostrata has 48 or 50 ver- 
tebrse, and II pairs of ribs; Physalus antiquorum 61 or 62 
vertebrae and 15 ribs; Megaptera longimana 53 vertebrae and 14 
ribs; Balcena mysticetus 54 vertebrae and 12-13 ribs. 
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