THE ELASMOBRANCH FISHES 



101 



lateral levator (llsr). The lateral levator labii has its origin behind the angle 

 of the ethmoidal region and is inserted on the process of the quadrate. The 

 median head arises as a broader muscle near the preorbital process and passes 

 as a tendon around the angle of the mouth to join the mandil)ular muscle as in 

 Acanthias. 



A more complex condition is reached in Rhinobatis and in Baja. In the 

 former there are four (or even five) parts to the muscle, and in the latter five 

 parts are cliaracteristicall}- present. In Raja (fig. 107b) the first division of 

 the muscle Us} represents the me- 



dian division of the muscle in Tor- 

 pedo. There is a second muscle (fig. 

 107b, Us.-) M'hich is large in Raja 

 and which holds a peculiar position 

 in Rhinobatis, being surrounded at 

 its base by the mandibular muscle 

 soon to be described. A third slip 

 (lls.^) is isolated, and a fourth and 

 a fifth ( ?) join the mandibular 

 muscle. 



The levator maxillae superioris 

 muscle in Acanthias {l.mx., fig. 104) 

 has its origin from the postorbital 

 processes and supraotic crest, and 

 passes downward in common with 

 the first dorsal constrictor, the fibers 

 of the latter lying directly against 

 the spiracle and the fillers of the 

 former (levator maxillae) being 

 those of the anterior group. The 

 levator maxillae is inserted on the 



093 



Fig. 103. Development of the muscles to the 

 eye, AcantJiias, right, median view. (From 

 I^amb.) 



a.r.. anterior rectus; cl.g., ciliary ganglion 

 of fifth nerve; g.g., gasserian ganglion; i.o., 

 inferior oblique; i.r., inferior rectus; o.p., 

 optic pedicel; op.V, ophthalmicus profundus; 

 p.r., external or posterior rectus; s.o., supe- 

 rior oblique; os.V and VII, ophthalmicus su- 

 perficialis branches of tlie fifth and seventh 

 nerves; s.r., superior rectus; /// and VI, ocu- 

 lomotor and aljducens nerves respectively. 



palatoquadrate. In Carcharias, how- 

 ever, in addition to its postorbital relations, it extends its origin anteriorly 

 along almost the whole of the supraorbital crest. In the rays, this muscle and 

 the first dorsal constrictor are distinct and separate. In Torpedo {l.mx., fig. 

 105a) the levator maxillae is well defined and runs far forward to be inserted 

 on the median palatal part of the palatoquadrate. In Rhinobatis it is much 

 broader than in Torpedo and is inserted still farther forward. In Raja {l.)iix., 

 fig. 105b) it arises by two heads, a superior and an inferior; the fibers of the 

 two unite anteriorly, whereupon insertion is made on the palatine part of the 

 palatoquadrate cartilage. 



Superficial Constrictors op Pharynx 



The superficial constrictor muscles vary considerably from those studied in 

 Heptanchus. These muscles in pentanchid Elasmobranchs are six in number. 



