834 



OSSEOUS SYSTEM. (CoMP. ANAT.) 



of their life a true branchial apparatus, which 

 subsequently becomes absorbed to give place 

 to thoracic or pulmonary respiration, and 

 consequently they are furnished in the first 

 portion of their existence with the hyoid 

 system of a fish, which, passing through dif- 

 ferent phases of gradually diminishing com- 

 plexity, is slowly converted into the simple 

 form it presents in their mature or adult 

 condition. So diversified, in fact, is this por- 

 tion of the osseous skeleton in the different 

 classes of Vertebrata, that the anatomist only 

 acquainted with human osteology would never 

 be able to recognise the analogy between what 

 he sees in man and the condition in which it 

 exists in its more complicated slates, or at all 

 understand the metamorphosis which it un- 

 dergoes in the embryo of Mammalia, without 

 tracing it through all its forms, as we shall 

 now proceed to do with as much brevity as is 

 compatible with our subject. 



In the Fish the os hyoides is situated as in 

 all the other Vertebrata, and is composed of 

 twelve bones. It consists of two branches, 

 each made up of five distinct elements, namely, 

 the styloid bone (29), which suspends it to the 

 temporal; two broad lateral pieces (fig. 436, 

 37 and 38) placed one behind the other, and 

 two small bones (39 and 40) placed one above 

 the other at the anterior extremity of each 

 branch, and forming with their fellows of the 

 opposite side a kind of symphysis uniting the 

 two halves of the bone. In front of this sym- 

 physis is a single bone, the lingual (41) situ- 

 ated as in Birds and Reptiles, and behind in 

 the angle formed by the union of the two 

 branches another azygos piece representing the 

 tail of the os hyoides so distinct in Lizards and 

 in Birds. This latter piece becoming joined to 

 the symphysis of the humeral bones forms the 

 isthmus that inferiorly separates the two bran- 

 chial apertures of the fish. 



Appended to the inferior and external mar- 

 gin of each branch of the os hyoides of a fish, 

 are the branchiostegous rays (jig- 437, 43), 

 destined to support the branchiostegous mem- 

 brane that completes the gill-covers. These 

 are very various both in number and form in 

 different fishes ; they are fixed to the os hy- 

 oides by distinct articulations, sometimes by 

 simple ligaments. Autenrieth and Geoffrey 

 suppose these branchiostegous rays to be the 

 representatives of sternal ribs, but doubtless 

 they belong rather to the exo-skeleton. 



To facilitate, however, a comparison between 

 the above complicated series of bones and the 

 corresponding pieces met with in other classes, 

 it will be advisable to lay before the reader the 

 result of the elaborate analysis of this part of 

 the skeleton made by GeofTroy St. Hilaire, 

 whose names applied to the various elements 

 composing it are not only classically elegant, 

 but from their simplicity will save much useless 

 circumlocution. When complete, the distin- 

 guished anatomist alluded to considers the 

 o hyoides to consist of the following parts : 

 The body or busihyal piece, forming the central 

 portion of the fabric ; the urohyal or tail of 

 the os hyoides (Jig. 437, 42); the entofiyal, 



a piece sometimes interposed between the two 

 former; two glosso/n/ala or posterior cornua ; 

 two apohyuls (39) forming the first pieces of the 

 anterior or styloid cornua; two ceratohyals(40) 

 forming the second pieces of these branches ; 

 and lastly, two stylohyals (29), which are re- 

 presented in the human subject by the styloid 

 processes of the temporal bone. 



Appended to this hyoid apparatus are a 

 series of lateral arches emulating in their im- 

 portance the ribs in the water-breathing Ver- 

 tebrata, and indeed somewhat resembling them 

 in structure and arrangement, along which run 

 the branchial vessels to the gills, and subse- 

 quently from the gills to form the aorta. These 

 arches have in fact, by some continental anato- 

 mists, been actually looked upon as repre- 

 senting the thorax of Vertebrata that respire 

 the air, but with little reason, as must be evi- 

 dent on considering how, as the real thorax is 

 called into play, these are gradually absorbed 

 and disappear. 



The branchial arches of a fish, from which 

 are suspended the branchial fringes, consist on 

 each side of four chains of bones adherent by 

 their inferior extremities to an intermediate 

 series of ossicles, which is connected ante- 

 riorly with the symphysis of the os hyoides 

 between the four anterior elements of that bone 

 and above its tail. Superiorly the branchial 

 arches are fixed by a ligamentous attachment 

 beneath the cranium. 



The series of intermediate bones with which 

 the pairs of branchial arches are connected in- 

 feriorly, are placed behind the lingual and are 

 three in number, forming a kind of little ster- 

 num to the hyoid apparatus. Each of the 

 branchial arches consists of a superior and in- 

 ferior portion that are moveable upon each 

 other. The inferior portion (Jig. 437, 58) is 

 that connected with the intermediate chain of 

 bones, and in the anterior three pairs of arches 

 this is formed of two pieces. The posterior 

 pair has this part composed of only one piece. 

 The upper portions of the branchial arches 

 are made up of a single bone. The three 

 posterior (fig. 437, 61) support the pharyn- 

 geal bones (fig. 437, 62), while the anterior is 

 attached to the skull by the intervention of a 

 little style (59), which might be regarded as 

 the pharyngeal bone belonging to this pair. 



Internally all the branchial arches are pro- 

 vided with osseous plates or ridges which are 

 generally covered with teeth. These perform 

 in some degree the function of the epiglottis 

 of Mammalia, inasmuch as they prevent any- 

 thing taken into the mouth from getting into 

 the gills along with the water as it passes to the 

 respiratory organs. 



The pharyngeal bones are peculiar to Fishes, 

 and are situated in the throat, where they 

 powerfully assist in masticating the food. There 

 are usually two inferior and six superior. The 

 inferior (Jig. 437, 56) are attached behind the 

 branchiae in the angle formed by the last pair 

 of branchial arches; they are generally of a 

 triangular shape, and form a kind of floor to 

 the pharynx. The upper pieces (Jig. 437, 

 62) are three in number on each side, each 



