Miscellaneous. 439 



and its mitlines become distinctly marked. It represents the umbi- 

 lical vesicle, which is much less developed in most of the unguiculate 

 Mammalia. 



In the genera Lejnlemio', Hajxdemur, and Chirorjaleus the placenta 

 presents the same characters. 



From this investigation it follows that the tunics of the embryo 

 of the Lemuroidea are constructed upon a plan of which we are 

 acquainted with no other example in the class of Mammalia. This 

 special type departs much more from that of Man, the Monkeys, 

 Chiroptera, Insectivora, and Rodentia than from that which is proper 

 to the Carnivora ; for if we suppose the caudal pole of the ovum in 

 the dog to be invaded by the villosities of the i^lacenta, we have 

 almost a realization of the special characters of the ovum of the 

 Lemuroidea ; and I may add that the arrangement of the umbilical 

 vesicle is very nearly the same in the two types, whereas in the 

 Monkeys it is completely different. 



These important embryologicnl characters are in accordance with 

 those furnished by the brain, the skull, the dental system, and the 

 hands. 



The brain of the most highly organized Lemuroidea is but little 

 developed behind ; and instead of entirely covering the cerebellum, 

 as it does in the Monkeys, it leaves a more or less considerable por- 

 tion of that organ exposed. Gratiolet, also, had previously noticed 

 that the characters of the enccphalon of the Lemuroidea separate 

 these animals clearly from all the Primates. 



The orbit, which, in the group of the Monkeys, is completely 

 closed outwardly and isolated from the temporal fossa, communicates 

 broadly -with the latter in all the genera of Lemuroidea, which 

 gives their skull a certain resemblance to that of the Carnivora. 



The teeth which arm the lower jaw in front are formed very dif- 

 ferently in the Monkeys and the Lemuroidea. In the former the 

 distinction between the canines and the incisors is very clear, and 

 the latter are neaidy vertical ; in the Lemuroidea they are narrow, 

 pressed against each other like a comb, laid almost horizontally, and 

 their forms are so similar that certain zoologists regard them as 

 being all incisors, whereas in reality those of the third pair repre- 

 sent the canines of other Mammalia. 



The hands, of which the thumb is always well developed, and 

 almost constantly opposable to the other digits, do not present the 

 characters of those of the Monkeys ; they are admirably constructed 

 for climbing, but unfitted for the prehension of articles of food. It 

 is with the mouth that these animals usually lay hold of their nou- 

 rishment, unless they emploj' their united hands for this purpose, 

 as the squirrels and many rodents are in the habit of doing. The 

 fingers, instead of tapering towards the end, like those of Monkeys, 

 are generally enlarged in their terminal portion, forming discoidal 

 pads which the nail does not entirely cover. Lastly, the index of the 

 posterior hand terminates, as is well-known, in a regular claw. 



If, in the classification of the Mammalia, we desire that the na- 

 tural groups, denominated orders, should have the same zoological 



33* 



