258 report— 1846. 



are formed by the gradually bent-down ribs*, which aje formed in the 

 abdomen either by unusally elongated 'parapophyses' (if they be inter- 

 preted by the condition of those elements in the cod-fish), or by pleurapo- 

 physes articulated directly to the fibrous sheath of the notochord ; which 

 interpretation of the mode of formation of the haemal arches is supported by 

 Professor Midler's discovery of the nature of those arches in the Lepidosteus\. 

 Whether we adopt the analogy of the Anacanthini, or the Ganoidei (and 

 the general affinity of the Protopteri to the ganoids would incline the choice 

 to the latter), the constitution of the haemal arches in the lepidosiren is 

 strictly piscine ; at least if we take the skeleton of the tailed batrachia 

 (fig. 28) as our guide to the homology of the caudal inferior arches in 

 higher reptiles and mammals. The unusual size and length of the abdo- 

 minal parapophyses in the cod-tribe (Gadidce), the flat-fishes (Pleuronectidce), 

 and the genus Ophidium, evinces the natural character of the order Anacan- 

 thini, in which they have been grouped together by Professor Miiller: the 

 pleurapophyses are, conversely, very short and slender in this order. In all 

 bony fishes the costal arch in the abdomen is completed by the aponeurotic 

 septa between the ventral portions of the myocommata;}:, which there repre- 

 sent the ' haemapophyses' (cartilagines costce, inscriptiones tendinece muse, recti 

 abdominis of anthropotomy). Indeed, when we reflect that the trunk of 

 the fish, by reason of the advanced position of the heart and breathing organs, 

 answers to the abdominal and caudal regions of the trunk of higher verte- 

 brates, we could hardly expect the typical vertebra to be there carried out in 

 osseous tissue ; but rather be prepared to find the haemapophyses retaining 

 the same primitive histological state which they present in the abdomen of 

 mammals and man (fig. 25, h"). 



Immediately behind the coracoid arch, it is usual to find a long and slender 

 rib-like bone, sometimes composed of two pieces, on each side ; it gives a 

 firmer implantation to the portion of the myocommata immediately behind 

 the pectoral fin ; and is obviously the ossified serial homologue of the haerna- 

 pophysial aponeuroses between the succeeding myocommata. It is usually 

 detached from its centrum and articulated superiorly to the inner side of the 

 coracoid : when it rises higher, as in the Batrachus, it becomes attached to 

 the atlas, and in the Argyreiosus vomer it meets and joins its fellow below, 

 forming a true inverted or haemal arch, parallel with, but more slender than 

 the coracoid arch. No other idea of the general homology of this arch pre- 

 sents itself than as a haemal one, completing the costal arch as an ossified 

 haemapophysis, differing from the typical vertebra (fig. 15) only by the non- 

 development of a sternum or haemal spine : and there appears to be as little 

 ground for hesitation as to the particular segment of the endoskeleton to which 

 to refer this costal or inverted arch ; its immediate succession to the correspond- 

 ing arch attached to the occiput, as well as the occasional direct attachment, 

 indicating that segment to be the atlas or first vertebra of the trunk. 



The best-marked general character of the vertebral column of the trunk in 

 the class Pisces is that which Professor J. Miiller first pointed out ; viz. the 

 formation of the haemal arches in the tail by the gradual bending down and 

 coalescence of the parapophyses ; the exceptions being offered by the ganoid 

 polypterus and lepidosteus and the protopterous lepidosiren. The pleurapo- 

 physes are, sometimes, continued in ordinary osseous fishes from the parapo- 

 physes after the transmutation of these into the haemal arches. The dory, 



* Linn. Trans, vol. xviii. pi. 23, fig. 4, x x. 



t Remarks on the Structure of the Ganoidei, in Taylor's Scientific Memoirs, vol. iv. 

 p. 551. 



X Lectures on Yertebrata, 1S46, p. 163, fig. 44, h p. 



