THE ELASMOBRANCII P^TSHES 



93 



Tliere are in Heptanclius inaculatus two levator labiales muscles. One of 

 these {lls.^, fig. 92) arises from the median side of the antorbital process, 

 passes backward over the angle of the jaw, and as a fibrous band divides the 

 adductor mandibulae into dorsal and ventral parts. The other labialis (Us.) 

 arises from the cranium in front of the antorbital process and nearer the mid- 

 ventral line as a wide and loose band of connective tissue ; it passes under the 

 orbit, and over the adductor mandibulae to be inserted at the angle of the jaw. 



ADDUCTORS 



The adductor mandibulae (a.md., fig. 92) is an immense and complex muscle 

 which closes the jaws. Superficially it is divided into a dorsal and a ventral 

 part by the insertion of the first labialis muscle. The fibers of the adductor 

 mandibulae arise from the 

 quadrate and are inserted in 

 two groups : first, a smaller 

 deep posterior group is in- 

 serted directly on the man- 

 dible; second, a major group 

 joins the tendon of the la- 

 bialis, and fibers are then 

 continued from the lal)ialis 

 tendon ventrally to insert on 

 the mandible. The insertion 

 in general is somewhat ob- 

 scured bj- a fibrous capsule 

 over the ventral part of the 

 muscle. 



An adductor is absent 

 from the hyoid, but adductors similar to the deep posterior part of the adduc- 

 tor mandibulae are present on all the branchial arches. These muscles have 

 their origin in a groove on the inner side of the epibranchial (see p. 149, fig. 

 143, ad.) and join the ceratobranchial cartilage. They act in closing the bran- 

 chial arch and hence in spreading the cartilaginous branchial rays to enlarge 

 the gill pocket. 



Ventral Longitudinal Muscles 



Fig. 94. Interareuales muscles, Heptanchii-'i maculatus. 

 (From Davidson.) 



eh}''', first to seventh epibrancliial cartilages ; ia.d}'^, 

 first to fifth dorsal interareuales ; ia.l}''^, first to sixth 

 lateral interareuales; ph}~^, first to sixth pharyngo- 

 branchial cartilages ; s.sp., subspinalis muscle. 



The last group of muscles to be considered in the region of the pharynx is com- 

 posed of the hy]:)ol)ranchial or ventral longitudinal muscles. These are forward 

 continuations of the ventral body musculature, the segmental nature of which 

 is seen in a series of myosepta in the coracoarcuales {car., fig. 95). The 

 arcuales communes take origin from the coracoid cartilage and are inserted 

 on the heavy connective tissue which forms the floor of the pericardial cavity. 

 The coracomandibularis (c.md.) arises from fascia above and between the 

 anterior projection of the arcuales and passes forward as a large band to be 



