218 ANATOMY OF THE RABBIT 



At the same time, it requires that a synthesis be made of the 

 observations in various places in order that a conception of each 

 system as a whole as well as of the total organism be obtained. 



I. EXTERNAL FEATURES 



The external structures, subdivisions of the body, and super- 

 ficial skeletal points may be made out as follows: 



1. The division of the body into head (caput), neck (collum), 

 trunk (truncus), tail (cauda), and anterior and posterior 

 limbs or extremities (extremitates). 



2. In the head: 



(a) The division into a posterior, cranial portion (cranium), 

 and an anterior, facial portion (facies). 



(b) The mouth (os), bounded by the cleft upper lip (labium 

 superius) and the undivided lower lip (labium inferius). 

 The external opening of the mouth is relatively narrow, 

 having been reduced during development by the growth 

 forward of tissue from each side to form the cheek. 



(c) The large sensory hairs or vibrissae. 



(d) The nose (nasus) and its ovoid external apertures, the 

 nostrils (nares anteriores), which connect with the upper 

 end of the groove dividing the upper lip into right and left 

 halves and have the skin at their inner margins slightly 

 folded. 



(e) The eye (oculus) and its coverings, the eyelids, including 

 the upper eyelid (palpebra superior), the lower eyelid 

 (palpebra inferior), and the third eyelid or nictitating 

 membrane (palpebra tertia). The third eyelid occupies 

 the anterior angle of the eye, and is comparable to the 

 conjunctival fold of the human eye. It is stiffened by a 

 thin plate of flexible cartilage covered with a layer of 

 glandular tissue and moulded to the exact curvature of 

 the surface of the eyeball. 



The eyes of the rabbit look more nearly straight laterally than do 

 those of most mammals, the angle between the visual axes of the two 

 eyes after death having been found to be over 141°. The fields of vision 



