94 DESCRIPTIONS OF PREPARATIONS. 



series with another, closes the gill-clefts and prevents the passage of foreign 

 bodies of any size. 



The vertebral column consists of forty-two vertebrae, of which twenty- 

 two are dorsal and twenty caudal. There are no other regions differentiated 

 in the backbone of a fish. Successive vertebrae articulate one with another 

 by the edges of the centra, which are united by ligaments. In the majority 

 of vertebrae a process springs from the base of the neural arch on each side 

 and articulates with the arch of the vertebra preceding. The neural arches 

 are continuous with the centra, and are prolonged dorsally into neural 

 spines. Lateral projections, or inferior, i.e. haemal arches, as it appears 

 from development, project from the centrum of the eighth and following 

 vertebrae. They increase in length and are turned more and more ventrally 

 in the posterior dorsal vertebrae. The processes of the two last dorsal ver- 

 tebrae have the ribs united to them, as is the case in the caudal series, 

 where the ventral ends of the ribs unite and inclose the caudal canal, which 

 lodges the caudal artery and vein. This is the case as far as the last or 

 terminal caudal vertebra, which bears solid inferior arches, to either side 

 of which pass the two vessels into which the caudal artery and vein divide. 

 The two last caudal vertebrae are modified. The last but one has a short 

 expanded neural, and a long inferior arch. The last has the centrum pro- 

 longed into the urostyle the ossified and undivided sheath of the notochord 

 which is bent upwards dorsally at a sharp angle and incloses the termina- 

 tion of the notochordal cartilage. It has a long, low neural arch and six 

 inferior or haemal arches, expanded and flattened, divided by an interval 

 into two groups of three arches apiece, one anterior, the other posterior. To 

 the neural arches of these two terminal vertebrae are attached three long 

 and somewhat broad ' false ' spines, as they are called. These, with the 

 haemal arches, carry the rays of the caudal fin. Simple curved and free 

 ribs are carried on the lateral processes of the dorsal vertebrae except the 

 two last. These ribs bend ventrally but do not meet, and in the Perch, as 

 in all other fish, there is no sternum. Certain of the anterior ribs have 

 epipleural bones attached to them at some little distance from their vertebral 

 ends. These bones radiate outwards into the myocommata or connective 

 tissue septa uniting successive muscular segments or myomeres. 



The Perch has four fins belonging to the median or azygos system. 

 These fins, as in all fish, are supported by fin-rays, ossified in the Teleostei. 

 The four fins are the first and second dorsal, the caudal, and an anal, which 

 is in position ventral. The dorsal and anal fins are supported by a series 

 of bones, ' fin-bearers ' or ' interspinal ' bones, which in the case of the dorsal 

 fins alternate with the neural arches ; in the case of the anal fin with the 

 inferior arches. These bones lie between the muscle-masses of the right 

 and left halves of the body respectively. The folds of integument which 

 constitute the fins proper, are supported by bony 'fin-rays.' There are 



