32 



coraco-branchials. The third aortic branch passes between the sec- 

 ond and third coraco-branchials. The fourth aortic branch passes 

 between the third and fourth coraco-branchials. 



Expose the dorsal ends of the gill arches by clearing away 

 muscles and other tissues between the gill pouches and the spinal 

 column. Two sets of four small muscles (interarcuales) will be 

 found connected with the branchial cartilages. The second, third 

 and fourth medial interarcuales extend from the posterior surfaces 

 of pharyngo-branchial cartilages 1, 2, and 3, to the dorsal surfaces 

 of pharyngo-branchials 2, 3, 4, and 5. The first medial inter- 

 arcuale arises from the under surface of the cranium and inserts on 

 the upper end of the first pharyngo-branchial. 



The lateral interarcuales lie immediately below the medials. The 

 first has a double origin, most of the fibres arising from the lower 

 part of the posterior edge of the first pharyngo-branchial; a smaller 

 bundle from the anterior edge of the second pharyngo-branchial. 

 Its insertion is along the dorsal surface of the first epibranchial 

 cartilage. The second and third lateral inter-arcuales are like the 

 first, but since the fourth and fifth pharyngo-branchials are fused, 

 the origin of the fourth lateral interarcuale is not divided. 



The circular muscles of the oesophagus are strongly attached to 

 the last pharyngo-branchial. 



MUSCULATURE OF THE PECTORAL FIN. The dorsal muscle of the 

 fin (levator-retractor) arises mostly from the scapular portion of 

 the girdle, with a small part arising from the fascia covering the 

 lateral musculature of the body. It is attached in fasciculi to the 

 dorsal surfaces of the cartilaginous rays. The ventral muscle (de- 

 pressor-protractor] arises from the median portion of the girdle and 

 is inserted upon the cartilaginous rays in similar fasciculi. A por- 

 tion of the lateral body muscles is inserted upon the scapular por- 

 tion of the girdle. 



MUSCULATURE OF THE PELVIC FIN. Ventral surface: An ad- 

 ductor muscle has origin upon the postero-lateral edge of the girdle; 

 it is inserted upon the antero-medial surface of the basal cartilage 

 of the fin. The depressor muscle consists of small fasciculi, each 

 corresponding to a cartilaginous ray. They arise from the postero- 

 lateral surface of the basal cartilage and are inserted upon the distal 

 extremities of the rays. 



Dorsal surface: The abductor arises from the fascia covering 

 the trunk muscles, and inserts upon the fascia covering the intrinsic 

 muscles of the dorsal side of the fin. These latter (levatores) are 

 arranged in exactly the same manner as the fasciculi of the de- 

 pressor. 



MUSCULATURE OF THE DORSAL FINS. A sheet of muscle is at- 

 tached to each side of the anterior dorsal fin, extending nearly up 

 to the bases of the dermal fin-rays. This muscle passes downward 

 between the dorsal body musculature of the two sides. Part of the 

 fibres arise from the fasciae covering the medial surfaces of the 

 body muscles, part from the basal cartilage of the fin itself. They 

 are inserted upon the lateral surfaces of the broad cartilaginous fin- 

 rays. The muscles of the posterior dorsal fin are exactly similar in 

 arrangement. 



MUSCULATURE OF THE CAUDAL FIN. There is no special muscu- 

 lature for the dorsal portion. A narrow, band-like muscle is found 

 on each side of the ventral portion, widest above the triangular 

 ventral lobe. The fibres of this muscle arise upon the flattened, 

 expanded ends of the haemal spines. They pass obliquely backward 

 and upward to be inserted in the fascia underlying the skin. 



