1918] Bavidson: Tliv Musc\datur(of Hfptanchus iuaculatus 163 



The second or rectus group consists of four muscles which originate 

 from the posterior part of the orbit at the base of the optic pedicel. 

 The dorsal member of this group is known as the superior rectus 

 {s. v.), the ventral as the inferior rectus (/. /•.), the anterior and 

 posterior as anterior {a.r.) and posterior recti {p. r.) respectively. 

 They pass outward and forward and are inserted on the eyeball in 

 positions according to their naming. The function of the eye-muscles 

 is to turn the eyeball in the orbit. 



II. Muscles of the Parietal Fossa (fig. 6). In connection with a 

 small shield-shaped organ present in the parietal fossa of Heptaitclius 



Fig. 5 Fig. 6 



Fig. 5. Eye-muscles, Heptanchus maculatus, dorsal view (X 1). a.r., 

 anterior rectus muscle; i. o., inferior oblique muscle; ('. ;■., inferior rectus muscle; 

 H. 77, optic nerve; o. p., optic pedicel; p. r., posterior rectus muscle; .s. o., superior 

 oblique muscle; s. r., superior rectus muscle. 



Fig. 6. Organ over parietal fossa, Heptanchus maculatus, dorsal view. (X 3). 

 e. d., endolymphatic duct; o., organ in fossa; p.m.. parietal muscle. 



maculatus, is a pair of small short muscles, the parietal muscles 

 (p.m.). They have their origin dorsally on the cranium and the 

 anterior part of the dorsal longitudinal muscles, just posterior to the 

 parietal fossa. Their course is anterior and medial and they are 

 inserted postero-laterally on the parietal organ. It seems possible 

 that these muscles constrict this sac-like organ. 



Appendicular Musculature 

 There are two types of fins found in the sharks, paired and un- 

 paired. The paired fins include the pectorals and pelvics, the unpaired 

 the dorsal, anal, and the caudal. Their musclature is similar and 



