ELASMOBRANCIIS. 
1073 
or, as in the Rays (fig. 300, nipt), by a more exten- 
sive cartilage, stretching from the lower part of the 
hyomandibular bone to the postorbital region. Outside 
this pharyngeal and masticatory apparatus there lie as 
a rule three (sometimes — as in several Sharks [fig. 
298, 1ms and Imi] — only two, sometimes — as in the 
Rays — none) pairs of labial cartilages, the two largest 
and most constant meeting at each corner of the mouth. 
Where they are all present, two of them ( Ims ) lie, one 
before and below the other, on the outside of the palato- 
qu ad rate cartilage, the third (Imi) outside the Meckelian 
cartilage. The former two answer to the intermaxil- 
laries and maxillaries, the latter is homologous with 
the mandible. 
i'he position occupied in relation to the said ske- 
letal parts by these cartilages recurs in a number of 
cartilaginous rods (tig. 298, evs ), first described by 
Rathke", which lie in the skin between the gill-open- 
ings, forming the outer support of the above-mentioned 
cartilaginous rods in the branchiostegal membranes (fig. 
298, br). GegenbauiC called the first-mentioned rods 
outer gill-arches, and considered them, as Cuvier had 
partly done 0 , to lie vestiges of the more complex 
branchial arches of the Marsipobranchs. Parker'* called 
them extraviscerals or extr abranchials, and saw in them 
homologues of the shoulder-girdle (the scapulae and 
coracoid bones), as being extracostal growths. Where 
their development is highest, as in the majority of the 
Sharks, they consist of two parts, a dorsal and a ventral, 
which meet and are applied to each other throughout 
a greater or less portion of their extent. In several 
Sharks and in the Rays they either are rudimentary, or 
have only the ventral parts developed (tig. 298), or are 
entirely absent. The angular, hooked or forked ventral 
ends of these “outer gill-arches” are joined below, from 
one side of the body to the other, by an horizontally 
set, fibrous membrane; and in this manner is formed, 
under the hypobranchial (lowest, tigs. 298 and 300, hbr) 
and copular (bbr) parts of the true branchial arches, a 
special chamber, a prolongation of the pericardial cavity, 
to receive the heart with the conus arteriosus and, 
within an anterior division, the truncus arteriosus. 
The hyoid arch shows an entirely different com- 
position and suspension in the Sharks and Chiinaeras 
on the one hand and in the Rays on the other. In 
the former the true middle part ( ceratohyoic/eum , tigs. 
294 and 298, cliy) is suspended from the lower ex- 
tremity of the hyomandibular cartilage (hm), and these 
parts are united below, from one side of the body to 
the other, by the first copula ( basihyoideum , bhy). In 
the Rays the hyoid arch consists on each side, as a 
rule, of 3 or 4 parts, the lowest ( hypohyoideum , fig. 
300, hby), as well as the lowest part of the first branchial 
arch ( hyp abranchiate ), meeting the first copula ( bbi \ ). 
Among the remaining parts of the hyoid arch the 
ceratohyoid (chy) and epihyoid (ehy) are the most con- 
stant; the uppermost part ( sthy ), answering to the sty- 
lohyoid of the Teleosts, is either cartilaginous or re- 
presented by a ligament, and suspends the arch from 
the upper posterior angle of the hyomandibular cartilage. 
The true branchial arches consist as a rule of four 
parts on each side — the hypobranchial (hbr), the cera- 
tobranchial (cbr), the epibranchial (ebr), and the pha- 
ryngobranchial (phbr). But between the lowest parts 
(the hypobranchials) there appear in the Sharks, though 
their occurrence is irregular, unpaired pieces (copular 
parts), sometimes five in number. Only the hindmost 
and largest (bbr), under which the heart is situated, 
is constant, and this is always present in the Rays 
as well, where it attains a still greater development. 
Gill-rakers are usually wanting in the Elasmo- 
branchs; but two remarkable exceptions are formed by 
the largest Sharks known, the North Atlantic Basking 
Shark and the Whale-Shark (Rhinodon typicus) of the 
Cape of Good Hope and the Indian Ocean east of Africa. 
Like the whales, these Sharks live on small animals, and 
like the Teleosts that feed in the same way, they are 
furnished with a filtering apparatus (“gill-grating”, 
Steenstrup, see tig. 332, p. 1145), which separates the 
food from the water that pours from the mouth at 
the same time and finds an outlet through the gill- 
slits. This filtering apparatus is composed in the Bask- 
ing Shark 0 of tine, setiform, and dense gill-rakers, up 
to 6 inches long, the microscopical structure of which 
a Anat. Phil. Unters. Kiemenapp., Zungenb. Wirbelth. (1832), p. 83. 
b Unters. Vergl. Anat. Wirbelth., 3:tes Heft, p. 164. 
c Lemons, ed. 2, tom. VII, p. 307. 
d Trans. Zoo], Soc. Loud., vol. X, p. 212. 
e Gunnerus, Trondhj. Selsk. Skr., part. Ill (1765), p. 46; Foulis, Proc. Best. Soc. Nat. Hist. 1854, p. 203; Steenstr., Overs. D. 
Vid Selsk. Forh. 1873, No. 1, p. 47, tab. II. 
