168 LECTURE VII. 



The pubic arch supporting the ventral fins, is attached in the 

 Perch by a i^air of slender longitudinal muscles («') to the prolonged 

 haemal arch, sometimes called ' pelvis,' of the first caudal, and which, 

 in its course to the pubic arch, surrounds the anus : the length of 

 these muscles is moderate in the ventral fishes, considerable in the 

 thoracic, and extreme in the jugular fishes, in which they simulate 

 the ' recti abdominis.' It is probable that the external ' sphincter 

 ani ' of Mammals is the reduced homologue of these muscles. In 

 general homology they must be viewed as the lowest ventral strip of 

 a single myocomma, more or less developed in accommodation to the 

 varying distance between the last abdominal and first caudal, its 

 proper, hasmal arches, which variation relates to the ofiice required 

 to be performed by the ventral fins, or appendages of the last abdomi- 

 nal haemal arch, in the different species of fishes. The protractors of 

 the pubic arch ai'e attached, Avhen present, to tlie apex of the coracoid 

 arch. Transverse muscles extend from one pubic bone to the other ; 

 and similarly disposed special muscles serve to contract the span of 

 the mandibular and hyoidean arches. The levators and depressors 

 of the ventral fin are inserted, as in the pectorals, by as many 

 fasciculi as there are digital rays. 



The deeper seated fibres of the segments, which together constitute 

 the great lateral muscular masses of the trunk, alter slightly their 

 direction, and, in the abdomen, represent the ' intercostals,' passing 

 from one vertebral rib to another, and from one ajjoneurotic repre- 

 sentative of the sternal rib (inscriptio tendinea, h, p.) to another. 



The myocommata answering to the neural and hsemal spines of the 

 suppressed centres of the terminal caudal vertebrae, change their di- 

 rection like those spines, slightly diverging from the axis of the trunk 

 to be inserted into them : these modified terminal segments (z), by 

 their connection with the interlocked myocommata of the great lateral 

 masses, concentrate the cliief force of those muscles upon the caudal 

 fin. Special series of small dermal muscles are inserted into the rays 

 of the dorsal, anal, and caudal fins : the dorsal and anal rays have each 

 six fasciculi, two superficial («) and four deep-seated (y), which rise 

 from the expanded dagger-shaped interneural and interhaemal spines. 

 Beneath the muscles of the tail-fin which terminate the lateral series 

 of myocommata, there are long and slender fasciculi Avhich rise di- 

 rectly from the compressed coalesced bodies of tlie terminal caudal 

 vertebrae, and are inserted into the bases of the diverging rays. Other 

 small muscles pass from the bases to act upon the more distant parts 

 ,of the rays. Slender longitudinal muscles, ' supra carinales,' extend 

 along the midline of the back from the occiput to the first dorsal, and 



