ANATOMY OF VERTEBRATES. 75 



ments of the tympanic pedicle, which swings, like a pendulum, 

 from its point of suspension to the post-orbital process, fig. 29, g". 

 The hyoid arch is also small and simple in the Sturgeon. The 

 epi-hyal is short, and attached to near the upper end of the hypo- 

 tympanic. The cerato-hyal, fig. 62, 40, of thrice the length, is 

 expanded above, and is attached by ligament extending from that 

 part to near the joint of the lower jaw. The basi-hyal is a short 

 subcubical piece : it gives attachment anteriorly to cerato-hyals, 

 and posteriorly to the anterior basi-branchial and hypo-branchial 

 cartilages. 



The three first branchial arches consist of hypo-branchials, 

 progressively decreasing in size, of cerato-branchials, epi-bran- 

 chials, and pharyngo-branchials : the fourth arch consists of 

 cerato-branchials and epi-branchials : the fifth arch of cerato- 

 branchials only. The branchial cavity is closed by an opercular 

 dermal scale, d, 35, supported by the expanded tympanic cartilage, 

 m, fig. 62. 



The cartilaginous representative of the par-occipital projects 

 backward from each angle of the occiput. A triangular supra- 

 scapular cartilage, fig. 62, so, has the angles of its base slightly 

 produced, one being articulated to the end of the par-occipital, 

 the other to the ex-occipital region. To the apex is attached 

 the scapulo-coracoid arch, ib. 51, 52. The coracoid cartilage 

 expands as it descends, sends inward and forward a broad 

 wedge-shaped plate, and presents a large perforation at its thick 

 posterior part, answering probably to the perforated ulna of 

 osseous Fishes, here confluent with the arch. The pectoral fin 

 is articulated to the under part of this perforated projection : the 

 coracoid terminates by a broad thin plate beneath the pericardium, 

 where it is joined by strong aponeurosis to that of the opposite 

 coracoid. 



Special developement proceeds further in the skull of the 

 singular Acipenseroid, called ' paddle-fish' (Pla?iirostra Spatula). 

 It is remarkable for the rostral prolongation of the nasal and 

 vomerine bones, the rostrum being flattened horizontally and 

 expanded like the mandibles of a Spoonbill. The sides of the 

 rostrum are strengthened by a reticulate disposition of bony 

 matter in the form of stars, the rays of which anastomose. The 

 upper part of the cranium is less perfectly chondrified than in 

 the Sturgeon. There is a long vacuity between the frontal, 

 parietal, postfrontal and mastoid bones : the tympanic pedicle is a 

 simple elongated piece of bone expanded at both ends. The 

 mandibular and hyoidean arches are suspended by a short cartilage 



