ICHTHYOLOGY. 



215 



Introduc- geal arch, the rest branchial arches. The arches adhere by 

 tion. tlieir lower extremities to a chain of ossicles, and curving 

 Osteology, g^^ j]^gy ascend, nearly meet at the base of the cranium, to 

 which they are attached by ligamentous and cellular tissue. 

 Each of the first three branchial arches, independent of the 

 basal key bones, or basi-branchials, consists of three or four 

 pieces, which have a certain elastic or flexible movement 

 on each other. The lowest of these pieces is the short 

 hi/po-branchial ; the next, the long cerato-hrancliial, is 

 grooved on the outside, and supports the dentigerous pro- 

 cesses, or tubercles, named rakers. Above this is an epi- 

 hranchial similarly formed. To it, in the second and third 

 arches, the short, broad, dentiferous epi-branchial is com- 

 monly attached. The fourth arch consists of the cerato- 

 branchial, the epi-branchial, and the pharyngo-branchial 

 pieces. The fifth arch usually consists simply of the cerato- 

 branchial element, but in Anabcts it supports a pharyngo- 

 branchial. This last-named bone is often expanded, and 

 more or less dentiferous : it is termed by Cuvier " the in- 

 ferior pharyngeal bone," and the upper dentiferous portions 

 of the arches are called the superior pharyngeal bones." 

 In Cotlus, these superior bones are blended into one piece. 

 A peculiar development of the epi-branchial and pharyngo- 

 branchials of the first two or three arches, serves the office, 

 in a group of fishes, the Labi/rintliibranchii, of retaining 

 a supply of water for moistening the gills when the fishes 

 are temporarily out of their proper element. 



] . Scapular arch. This inverted cranial arch is attached 

 to the par-occipital ; or to that bone and the mastoid ; or to 

 the same bone and the petrosal, as in the Cod ; or to the 

 par-occipital and basi-occipital, being essentially the haemal 

 arch of the occipital bone, to which it is constantly attached 

 wholly or in part. In the Eels it is feebly developed, and 

 only loosely suspended behind the skull ; and in the Pla- 

 giostomes it is removed further back to a distance fi'om its 

 proper vertebra. Its superior piece is the supra-scapula, then 

 follows the scapula, and the arch is completed below by the 

 union of the frequently very strong and firm coracoid with 

 its fellow. The coracoids defend and support the heart, and 

 give attachment to the diaphragm, which separates the 

 pericardial and abdominal cavities. 



The scapular arch usually supports a diverging appendage 

 on each side, constituting the pectoral fin. The pectoral 

 fin rays are analogous to the fingers of the higher animals, 

 the lowest ray, when the fin is laid back to the side of the 

 fish, answering to the thumb. The bones which support 

 these rays are homologues of the bones of the fore ex- 

 tremities of the higher vertebrals, and have been named 

 accordingly. In the Cod tribe, and most other fishes, there 

 is, however, no separate representative of the humerus. 

 The radiits is of enormous size in the Lampris and in 

 Flying-fish. It is anchylosed to the ulna in Silurus for the 

 firmer support of the pectoral spine, and in Lophius, both 

 radius and ulna are extremely small, and connate with the 

 coracoid. The carpals, usually four or five, but sometimes 

 only two, progressively increase in length from the ulna to 

 the radial side. In the Wolf-fish they are broad flat bones. 

 The metacarpals and phalangeals are in the Cod twenty in 

 number, all soft-jointed, and sometimes bifurcate at the 

 distal end. 



In the osseous fishes the pectoral fins present a series of 

 modifications. In the Acanthopterygii the ulnar ray is a 

 hard unjointed spine. In the Gurnards, Choridactyles, 

 and several other genera of Sclerogenida, the three lower 

 rays are detached and firee, and there is reason to believe 

 that these rays are used like fingers as organs of touch when 



the animal swims close to the sandy bottom of the sea. Introduc- 

 The pectoral fins are very largely developed in the Exo- 

 ccetus; it is also large in Dactglopterus, Trigla, and Prio- 

 notus, as well as in several other forms of the Sclero- 

 genidcE. 



In the Cod and Carp there is a single styliform bone, 

 named the epi-coracoid, because it is attached to the upper 

 end of the coracoid. In the Perch, and most other fishes, 

 it consists of two pieces. In Centriscus scolopax, Argijrei- 

 osiis vomer and S/gatius, it is joined by its lower end to its 

 fellow, thus completing an inverted arch behind the sca- 

 pular one. The epi-coracoids are absent or are very slender 

 spines in the Wolf-fish, Mullet, Goby, Stickleback, Remora, 

 Cepola, Uranoscopus, the Blennies, Siluroids, and Apodal 

 fishes. The apodal Sandlance, however, possesses the epi- 

 coracoids. 



Ventral Jins. The rays of the ventral fins are supported 

 by two bones, which are named pubic bones, and represent 

 the lower part of an inverted haemal arch. In no fish is 

 this incomplete pelvic arch directly attached to the vertebral 

 column. In all fossil fishes belonging to deposits anterior 

 to the clialk, the ventrals are placed towards the posterior 

 end of the abdomen, and hence, and from the consideration 

 of the position of the rudiment of the ventral in the em- 

 bryo fish, it may be inferred that these pubic bones are the 

 haemapophyses of the last abdominal vertebra. In Acan- 

 thopteri the anterior ray of the ventral may be spinous. 



In the Malacopteri all the ventral rays are soft, multi- 

 articulate, and bifurcate. The normal position of the ven- 

 tral haemapophysis is under its proper vertebra, but the rela- 

 tive length of the pubic bones in different fishes, places them 

 under the abdomen, or pectoral fins, or gills ; hence Lin- 

 naeus's division of the fishes into abdominal, thoracic, and 

 jugular, and, when the ventrals are want- 

 ing, apodal. Cuvier substituted the term 

 subrachial for thoracic and jugular. The 

 ventrals are better developed in the Pla- 

 giostomes than in other fishes, and con- 

 nected with this fin, in the male Plagio- 

 stomes and Chimera, there is the peculiar 

 intromittent organ of generation named 

 the " clasper." 



In the Gobies (fig. 22) and Gowo- u-ted^-njra,s^ofj5^ 

 r«?/wc/(?/^, the ventrals are united to each Chinese flsb. 

 other by a membrane ; and in Cyclopterus, Gobiesox, and 



Fig a. 



Pig. 23. 

 Lepadogaster puniceus, a Biscobolo or Cyclopteroid. A sacking apparatus is 

 formed round the basis oftbc ventrals. 



Lepadogaster (fig. 23), they so united as to form a suc- 

 torial foot, by which these fish can attach themselves to a 

 rock. 



We have allotted more space to the skeleton of fishes 

 than our limits will permit us to devote to the rest of the 

 ichthyic structure, because the soft parts and dermal system 

 cannot be properly apprehended or referred to without a 

 competent knowledge of the bony or cartilaginous endo- 

 skeleton by which they are sustained.' 



' In adopting Professor Owen's osteological system, we have thought it proper, to avoid mistalce, to use his own words as often as 

 we could ; but as our extracts from his elaborate and exhaustive work are very compendious, and not always in the order he pursued in 

 his lectures, they are not marked by inverted commas as quotations. 



