84 



of the mastoid cartilage, the other to the exoccipital cartilage. The scapulo-coracoid cartilage 

 expands as it descends, sends inwards and forwards a broad wedge-shaped plate, and presents 

 a large perforation at its thick posterior part, immediately above the articulation of the pec- 

 toral fin. The expanded under part of the cartilage sends a thin plate inwards and forwards 

 and another outwards, which forms the lower boundary of a wide smooth groove below the 

 prominence supporting the pectoral fin : above this is another groove communicating by a 

 small foramen with the larger excavation above mentioned. 



The form of the upper piece and its connections answer to those of the suprascapula, but 

 there is no separate styliform scapular piece, as in the Osseous Fishes. 



Presented by Prof. Owen, F.R.S. 



375. A dried specimen of a young Acipenser Sturio, showing the external or dermal 



skeleton. 



There are five longitudinal rows of dermal bones on the trunk of the Sturgeon, one along 

 the mid-line of the back, two along the sides, and two along the belly ; but the lateral bones 

 are most numerous; these are continued over the operculaj flap to the plate which lies 

 between the eye and the nose. 



Hunterian. 



376. The palate-maxillary, mandibular and hyoidean arches of a large Sturgeon 

 (Acipenser Sturio). 



These are the only ossified parts of the endo-skeleton in this fish. The bones are num- 

 bered in accordance with those of the articulated skulls, and with Table I. The maxillary (21) 

 is extremely small, as in most osseous fishes. The premaxillaries (22) send a process out- 

 wards and downwards to the mandibular joint, where they are articulated to two small labial 

 bones. Each branch of the mandible consists of a single osseous piece. The palatine (20) 

 and pterygoid (24) bones are confluent. There is a small separate centre of ossification on 

 each side in the soft palate anterior to the pterygoids. The epihyals, ceratohyals and basi- 

 hyals are only partially ossified. 



Hunterian. 



377. The palate-maxillary and maudibular arches of a Sturgeon (Acipenser Sturio). 



The constituent bones are numbered as in Table I. Hunterian. 



378. One of the lateral dermal ganoid plates of a large Sturgeon (Acipenser Sturio). 



Hunterian. 



379. One of the median dorsal dermal ganoid plates of a Sturgeon (Acipenser Stu- 



rio) . it is the homologue of the dermoneural spine in ordinary Osseous Fishes. 



Hunterian. 



