166 LECTURE VII. 



Perch (j) ; and, in some fishes, also, from the aponeurotic septum 

 between the branchial and abdominal cavity, to the lateral and lower 

 parts of the cranium. The protractor scapulte in the Skate and 

 Torpedo (45. i) is of considerable length, in consequence of the back- 

 ward displacement of the scapular arch (s), and of great strength, by 

 reason of the enormous pectoral appendage which the arch sustains. 

 The representatives of dorsal and middle portions of a second cranial 

 myocomma, in the Perch, are seen in the protractor tympani (44. k) 

 and in the retractor maxillse (w) : a lower parallel subquadrate por- 

 tion of the same segment passes from the preoperculum and tympanic 

 pedicle to the coronoid process of the lower jaw, and forms the ' levator 

 mandibulse ' ( «). A cephalic continuation of the ventral segments of 

 the myocommata is recognisable in the fasciculus which passes for- 

 wards in part (g) directly from the subcoracoideus (d,f), in part 

 (y) from the coracoid itself, to the basi- and uro-hyals, and which, 

 if it does not perform, as Cuvier states, all the functions of the 

 sterno-hyoid, represents the muscle to which that name is given in 

 higher vertebrata, and proves it to be, in its general homology, the 

 ventral segment of a cranial myocomma. 



Other dismemberments of the cranial myocommata are modified to 

 act specially upon the branchial arches : one of these fasciculi is the 

 branchi-depressor (o) : it rises from the basi-hyal, and passes obliquely 

 backwards to be inserted into the pharyngeal or last branchial arch : 

 two other fasciculi rise from the coracoid, and converge to be similai'ly 

 inserted, forming the branchi-retractores (p, q). Several small fasciculi 

 from the sides of the cranium are inserted into the epibranchials 

 and the first two pharyngo-branchials, forming the branchi-levatores 

 (r). There are also several transverse and oblique muscles, peculiar 

 to the branchial arches. The ventral portion of the most anterior 

 of the myocommata extends between the apex of the hyoidean and 

 that of the mandibular arches : Cuvier recognises its sjiecial homo- 

 logy with the genio-hyoideus (h) : it protracts the hyoid arch ; it 

 retracts the mandibular arch ; and, when the lower jaw is left free 

 to move upon the tympanic pedicle, it depresses the jaw. There is 

 no digastricus or proper depressor of the mandible in Fishes. A 

 strong muscle (/) from the postfrontal is inserted into the pterygoid ; 

 and partly through that, and partly by direct insertion into the pre- 

 tympanic, it raises and protracts the tympanic pedicle. The oper- 

 culum, or fin of the tympanic pedicle, has a levator or extensor (k) 

 and a depressor muscle ; the one rises from the mastoid, the other 

 from the petrosal or alisphenoid. 



In the Angler each of the long rays of the branchiostegal fin has 



