SKELETON OF COMMON PERCH. 93 



ossifies as the articular (Ar.\ from which an angular (An.} is cut off, while 

 the median portion remains cartilaginous and rod-like. It is surrounded 

 by the dentary (D.\ a bone formed in membrane, and carrying teeth. The 

 hyoid cartilage of the embryo gives origin to a pharyngo-hyal element 

 which ossifies as the hyomandibular (ffm.) and symplectic (Sy.) bones. They 

 are connected with the bones of the jaw as well as with some others to be 

 described presently. The hyomandibular has two condyles for articulation 

 with the otic region (f in Fig. 8). It is a large bone and represents, accord- 

 ing to Kitchen Parker's most recent researches, the columella auris or stapes 

 of higher forms. The quadrate represents the element of the same name 

 in Amphibians, Reptiles, and Birds, and the incus of Mammals, while the 

 malleus of the last-named group corresponds to the articular of the fish, of 

 Amphibia and Sauropsida. A series of membrane bones well developed in 

 Teleostei and Ganoidei are attached to the posterior edge of the hyoman- 

 dibular and quadrate bones. These are the prae-operculum (P. Op.\ the 

 operculum (Op.}, the sub-operculum (S. Op.\ and the inter-operculum (/. Op.}. 

 They close in laterally the branchial cavity. The remaining portion of the 

 embryonic hyoidan cartilage gives origin to the interhyal or stylo-hyal 

 (S. h} which articulates between the hyomandibular and symplectic, the 

 epihyal (Ep. k}, the cerato-hyal (C. h.}, both large flat bones, and two 

 nodular hypo-hyals (H. h.}. The arches of the right and left side are united 

 by a median basi-hyals (B. k.} or entoglossal. A series of membrane bones, 

 the branchio-stegal rays (Bs. r.}, are attached to the epi-cerato-hyal. They 

 are formed in the membranous flap, which is a continuation of the opercular 

 apparatus to the hypo-hyal region. A thin median bone, the basi-bran- 

 chiostegal ( = urohyal of Huxley), not shown in the figure, projects back- 

 wards from the basi-hyal region towards the ventral ends of the clavicles, 

 so-called, with which it is connected by ligament. It underlies the ventral 

 aorta. 



The branchial arches are five in number on each side. In the median 

 ventral line, and immediately following the basi-hyal, are three basi-branchial 

 bones. The first arch consists, proceeding from its dorsal to its ventral end, 

 of a small pharyngo-branchial, or superior pharyngeal bone, an epi-branchial, 

 to which is articulated, at a sharp angle, a cerato-branchial followed by a 

 hypo-branchial. The three next arches have a similar composition. The 

 pharyngo-branchials are, however, both large and dentigerous. The hypo- 

 branchial element in the third arch is applied laterally to the last basi-bran- 

 chial, and is wanting altogether in the fourth arch. The fifth arch consists of 

 a single bone, probably homologous with a cerato-branchial. Osseous plates 

 bearing fine teeth are implanted on the anterior and posterior aspects of the 

 four first arches. These plates are carried by cartilaginous rods in the case 

 of the first cerato-branchial. The rods, known as gill-rakers, are present 

 in some fish on the following cerato-branchials. The interlocking of one 



