MAMMALIA. 
39 
second, third, and fourth permanent molars, and similar in form to the 
upper milk-molars, but the third is considerably larger than the third of the 
upper jaw. The milk-dentition of this species is : inc. pfEjp j ’ 
Thus JlaUciiocrus, Phoca, and Cystophora appear to agree in their milk- 
dentition ; so that the number of incisors and canines is the same as that of 
the permanent dentition, but that there are two milk-molars less on each 
side of the upper and lower jaws *. Further, from a study of the milk- 
dentition of these animals, it is evident that Owen was mistaken when he 
regarded three of their permanent molars as premolars ; such a division is 
easily explained from the form of those teeth, and was made at a time when 
the milk-dentition of Otaria only was known, and this very incompletely. 
In the present state of our knowledge we must divide these teeth into four 
premolars and one molar, and it is not improbable that also Otaria will be_ 
found to possess four preinblars when its miUr-dentition shall be better known 
than it is at present. 
Phoca harhata. Prof. Steenstrup explains the reasons which induce him to 
regard a fourth molar observed in a young example as a milk-tooth, against 
the views of Prof. Reinhardt mentioned below, note. Vidensk. Meddel. 
naturh. Foren. Kjobenh. (1864) 1865, pp. 270-274. 
Otaria hookeri. Mr. Bartlett has made some observations on a tamed male 
Sea-lion, showing the great docility of these animals ; it stands on all fours, 
and runs and jumps at a great rate. Ann. & Mag. Nat. Hist. 1865, vol. xv. 
p.496. 
UOSORES.' . 
^ Prof. Giebel treats of the foramen in the zfygomatic proeess, 
through which, in many Rodentia, a portion of the masseter 
passes. He examines its size, form, and position in the various 
groups, and comes to the conclusion that it may be used as a 
very good generic character, without being of a higher syste- 
matic value. Zeitschr. gesammt. Ntrwiss. xxv. 1865, pp. 427- 
432. 
^ Mus rattus. M. A. de lHsle has made researches into the ' 
affinity between Mus rattus and that form which has been dis- 
tinguished as Mus alexandrhms by previous zoologists. Ann. 
Sc. Nat. 1865, iv. pp. 173-222. A part of these researches 
consisted of breeding- experiments continued for thirty months, 
during which time he obtained 26 litters with 129 young ones. 
AVc must remark, however, that all the individuals experi- 
mented upon were European examples, chiefly from France ,* 
* Steenstrup observed in a young Phoca harhata (but not in P. grbnlandica 
or P. hispida), with the second teeth much advanced in development, but 
with the milk-teeth still present, a fourth tooth behind the third molar, which 
he regards as a milk-tooth, without deciding whether it belongs normally to 
the milk-dentition or not. Reinhardt regards it as a tooth ahnormally de^ 
veloped in that individual, and is inclined to refer it rather to the second than 
to the first dentition, on account of its form and size. 
