30 



MUSCULATURE OF THE HEAD AND NECK. On the lateral and ven- 

 tral surfaces of the neck the primary relations of the myomeres are 

 much modified by the development of numerous special muscles, 

 yet here and there traces of the metameric arrangement still show. 

 Immediately beneath the skin is a thin sheet of muscle covering 

 most of the ventral and lateral surfaces of the throat as far back as 

 the pectoral girdle. On the ventral surface a triangular space is 

 left in front of the pectoral bar; on the sides of the neck the sheet 

 extends back to the last gill-cleft; dorsally, it reaches to the upper 

 extremities of the gill pouches. This is the constrictor superficialis 

 muscle. It is attached to fasciae dorsally and ventrally, and to the 

 extra-branchial cartilages. 



The constrictor superficialis consists of six metameric segments. 

 The four posterior ones are distinctly limited by the gill-slits and 

 extra-branchial cartilages. The second is anterior to the first gill- 

 slit, the largest of all, with distinct dorsal and ventral portions ex- 

 tending forward above and below the jaws. The first is recognized 

 as consisting of two distinct parts, on the dorsal and ventral sur- 

 faces of the head. The dorsal portion is a small curved muscle on 

 the anterior wall of the spiracle, extending from the external sur- 

 face of the auditory capsule to the inner surface of the lower jaw. 

 It lies close against the levator marillae superioris (see below). On 

 the ventral surface of the throat the posterior constrictor muscles 

 of the two sides are separated by a large triangular area. In front 

 of this the ventral portions of the first and second constrictors meet 

 in a median aponeurosis, from which their fibres extend trans- 

 versely, those of the first to the mandibular cartilage, those of the 

 second to the hyoidean cartilage. The first constrictor lies ventral 

 or superficially to, and largely covers the second. Reflect the 

 first constrictor from the aponeurosis outward, and demonstrate 

 the two layers of muscle. It will be noted that the second to sixth 

 constrictors consist of united dorsal, lateral and ventral portions, 

 while the first is reduced to widely separated dorsal and ventral 

 parts. 



On each side of the head, just outside the angle of the mouth, 

 is a large, thick muscle arising from the lateral surface of the 

 cranium, and inserted upon the outer surface of the mandible, the 

 adductor mandibularis. 



In front of the small dorsal constrictor superficialis 1, and 

 scarcely separated from it, is the strong levator maxillae superioris, 

 which extends from the lateral surface of the auditory capsule to 

 the dorsal edge of the palatoquadrate cartilage. 



Eugaleus. The dorsal portion of the constrictor superficialis 2 reaches 

 above the spiracle to the postorbital process. Reflecting it, the adductor 

 hyomandibulae is seen behind the spiracle, arising from the upper part of the 

 side of the auditory capsule and inserted on the end of the hyomandibular 

 cartilage. The levator palpebrae inferioris arises under the origin of the levator 

 hyomandibulae, and passes forward and downward between the spiracle and 

 postorbital process, to insert in the posterior end of the lower eyelid. The 

 depressor palpebrae superioris arises from the fascia dorsal to the spiracle, 

 passes mediad to the levator palpebrae inferioris, upward and forward, to insert 

 in the posterior end of the upper eyelid. Remove these muscles. The infraor- 

 bital canal passes mediad to the muscles of the eyelids. The levator maxillae 

 superioris lies between the spiracle and the orbit. Behind it is a small slip 

 of muscle extending from the anterior wall of the spiracle to the lateral surface 

 of the auditory capsule which seems to represent the constrictor superficialis 

 dorsalis 1. 



A thin sheet of muscle covers the anterior face of each inter- 

 branchial septum. At the surface these pass into the constrictor 



