458 THE ANATOMY OF VEETEBRATED ANIMALS. 



flat nail. Tlie hallux differs in form from the other digits 

 of the foot, and is so disposed as to be capable of more 

 or less extensive motion in adduction and abdiiction ; and, 

 very generally, it is opi^osable to the other digits of the foot. 



The Primates are divisible into — a. the Lemuridie, b. the 

 Simiadce, and c. the Anthrojiidce. 



a. The first of these divisions, the Lemuridce, is more 

 widely separated, anatomically, from the other two, than 

 these are from one another,* and it contains some forms 

 which very closely ax^proximate to the Insectivora, while 

 others are nearly affined to the Rodentia. 



All the Lemuridce are habitually qnadripedal, have the 

 integument furry, and are usually provided with long tails 

 which are never prehensile. They are devoid of cheek 

 pouches and of callous patches upon the integument cover- 

 ing the ischia. 



The fore limbs are shorter than the hind limbs. In 

 the foot, the hallux is large and opposable, and the second 

 digit difi'ers from the rest in size, and in the claw-like 

 form of its nail. The fourth digit is usually longer than the 

 others, the difference being especially marked in the pes. 



In the skuU, the brain-case is small relatively to the face, 



and is contracted anteriorly. If a straight line drawn from 



a point midway between the occipital condyles, through the 



median plane of the skull, to the junction of the ethmoid 



and pi'esphenoid, in the floor of the cerebral cavity, be 



termed the basi-cranial axis; and if the planes of the 



cribriform plate of the ethmoid, of the tentorium cerebelli, 



and of the occipital foramen, be respectively termed the 



ethmoidal, tentwial, and occipital planes ; then, the greatest 



length of the cerebral cavity hardly exceeds the length 



of the basi-cranial axis; and the ethmoidal, tentorial, and 



occipital planes are very much inclined to that axis. The 



upper aperture of the lachrymal foi-amen lies upon the 



* On the strength of these differences M. Gratiolet relegated the 

 Lemurs to the Insectivora; and Mr. Mivart, in his valuable paper 

 *' On the Axial Skeleton in the Primates," published in the Proceedings 

 of the Zoological Society for 18.5n, divides the Primates into two sub- 

 orders, Lemuroidea and Anthropoidea. 



