PHYSIOLOGY, AND PATHOLOGY OF THE CHIMPANZEE. 325 



A fan-shapecl muscle separates from the platysma in the neck, 

 runs upwards behind the auricle and spreads out into bundles 

 which are attached to the back of the auricle, the occipital crest, 

 occipitalis muscle, and the deep fascia over the back of the neck. 

 Huge (42) has given a very elaborate account of the manner in 

 which the platysma enters into the other facial muscles. 



Occipito-frontalis (text-fig. 25) : — There are many differences of 

 opinion about this muscle. Tyson (60) and Traill (49) could not 

 detect it, Owen (39) found a trace of it, and Wilder (53) found 

 the muscle bellies small, but the aponeurosis was large. Ruge (42) 

 figured a very extensive muscle and a small aponeurosis. 



In my specimen the occipitalis arises from the middle two- 

 fourths of the occipital crest, but it is not divisible into two bellies 

 as in Man. The fibres pass forwards for nearly two inches and 

 end in a well-marked aponeurosis. The frontalis arises from the 

 supra-orbital ridges and space between, but is not so well- 

 marked as the occipitalis. It is very easily removed with the 

 skin. It blends with the orbicularis oculi. 



The Orbicular'is oculi (text-fig. 27 A) is divisible into orbital 

 and palpebral parts as in Man. The former arises from the inner 

 end of the frontal bone and the nasal process of the maxilla ; and 

 both muscles are united across the mid line. As it lies on the 

 bones bounding the orbit its upper part is strong and compact and 

 gives off a strong bundle of fibres from its lateral part to enter the 

 zygomatic mass (Z.M). The fibres on the lower boundary of 

 the orbit are arranged in loose bundles. The palpebral fibres run 

 from the internal tarsal ligament to the lateral tarsal raphe, and 

 are thickened close to the roots of the eyelashes, the thickened 

 parts being of greater dimensions than the ciliary bundles (C.B) 

 in Man. At the lateral tarsal raphe the orbital and palpebral 

 parts are continuous. The nerve-supply from the facial nerve is 

 shown in text-fig. 26. 



The lips and cheeks receive many muscles (text-fig. 25), most 

 of which, though thin, are of considerable superficial extent. 

 They are disposed in two layers as in Man, but the characters 

 are very different in a number of points. The superficial layer 

 is composed of the risorius, levator labii superioris, zygomatic 

 mass, orbicularis oris, triangularis and quadratus labii inferioris. 

 The deep layer consists of buccinator, depressor anguli oris, 

 incisivi, canini, mentales, and premolares. The risorius is com- 

 posed entirely of the upper part of the platysma, for no fibres 

 are derived from the fascia over the masseter muscle. It blends 

 with other muscles at the angle of the mouth. The levator labii 

 superioris (Lev. Lab. Sup) arises, under cover of the orbital 

 part of the orbicularis oculi, from the entire infra-orbital border 

 of the maxilla. It radiates in a fan- like manner and is inserted 

 into the entire length of the upper lip and upper border of the 

 alee nasi. The fibres forming the latter insertion correspond to 

 the levator labii superioris alseque nasi of Man. Many of the 

 fibres of the muscle are very thin. Champneys (11) states that it 



Prog. Zool. Soc.— 1923, No. XXII. 22 



