398 Bashford Dean Memorial Volume 



muscle, it appears surprisingly large considering the slenderness and flexibility of the 

 jaws. This is well shown in Gregory's drawing (Text-figure 64 herein) and is perhaps 

 exaggerated in Fiirbringer's (1903) Fig. 1, pi. XVI. Consideration of the large size of 

 this muscle strengthens the conviction that Chlamydoselachus is in the habit of seizing 

 and swallowing fairly large prey. In this case the superficial constrictor muscles (Text' 

 figure 70; also Allis, 1923, Fig. 46, pi. XVII, and Fig. 48, pi. XVIII) as well as practically 

 every other muscle of the oral and branchial region, may be brought into play to assist 

 in the act of swallowing which is finally completed by the constrictor of the esophagus. 

 The superficial constrictor muscles that run in the gill'flaps are thin (Text-figure 78, p. 421) 

 but they are broad and they overlap like the shingles on a roof, so that collectively they 

 may exert considerable pressure. It has already been noted that the labial cartilages 

 are held in place by strong ligaments and fascia; some of these cartilages serve for the 

 attachment of special muscles. Thus an integumental muscle, the protractor anguli 

 oris, has a tendon attached to the mandibular labial cartilage (Allis, 1923). The strong 

 levator labii superioris (Allis, 1923, pp. 183-184 and Fig. 15, pi. X) may assist the creature 

 in expanding the mouth opening while swallowing its prey. Of this muscle Allis says : 



The levator labii superioris, in all my specimens, is wholly independent of the adductor 

 mandibulae, my specimens apparently differing in this respect from those examined by 

 Fiirbringer (1903, p. 384) and Luther. The muscle arises by a relatively long tendon from 

 the ventro'postero-lateral corner of the ectethmoidal process, and running almost directly 

 posteriorly swells abruptly into a muscle body which is inserted on the anterior half of the 

 posterior upper labial, some of the fibers apparently being inserted in the adjacent tissue 

 of the upper Hp. The muscle is innervated, as both Fiirbringer and Luther have stated, 

 by a branch of the mandibularis trigemini which arises from that nerve shortly after its 

 separation from the maxillaris trigemini. 



In many selachians there is a fairly strong adductor muscle, related to the mandible, 

 which is usually referred to as the muscle add. gamma of Vetter's (1874) description. 

 In Chlamydoselachus, the long tendinous portion of this muscle is apparently represented 

 by a strong ligament, which has its origin on a little process of the anterior edge of the 

 hyomandibular and its insertion on the posterior edge of the postorbital process of the 

 cranium (Allis, 1923, p. 187 and Fig. 23, pi. XI). I quote the following from Allis, 1923, 

 pp. 187-188: 



Fiirbringer and Luther both say that this muscle is not found in Chlamydoselachus. 

 Fiirbringer accordingly considers it to be a secondary arrangement, possibly the beginning 

 of a differentiation of a superficial portion of the adductor mandibulae, such as is found in 

 Amia and in many teleosts. Luther (1909, p. 54) thinks it is developed from the most posterior 

 portion of the adductor, and he considers it to be an archaic feature (I.e., p. 64) notwith- 

 standing that he did not find it in either Chlamydoselachus, Echinorhynchus or Odontaspis. 

 In Squatina, it is to be noted, the muscle arises by a few fibers from the hyomandibula (Luther, 

 1909, p. 60). 



One is especially impressed by the differences, with respect to this muscle add. 

 gamma, between the closely related forms, Heptanchus and Chlamydoselachus. In 



