G16 ]Mr. T. P. Buist on the Development of 



part of the scapular region, which has itself many of the 

 characters o£ a proximal radial and carries two distal radials 

 with their fin-rays. The posterior margin of the cartilage is 

 convex and is in relation with twelve nodules of cartilage, 

 the distal radials, which bear the elements of the twelve 

 fin-rays. 



Between the coracoid at the proximal or antero-inferior 

 angle, and the scapula and the four radial elements which 

 occupy the distal or posterior border with the upper and 

 postero-iuferior angles, lies an intermediate region which 

 forms from a third to a half of the whole cartilage. This 

 "intermediate cartilage" is notable in that, although 

 practically absent in the adult in most teleosts, in the pipefish 

 it persists, and in the adult actually forms the greater part 

 of the coraco-scapular skeleton. 



The two nuchal plates appear to develop in the same 

 manner as the other plates of the body-armour. In the 

 21 mm. embryo they are found as a pair of small thin bony 

 scutes each enclosed in a well-defined " flattened sac" very 

 similar to that described by KazanefF*. Their development 

 is at a stage between Kazanefl'^s figures 4 and 5, and is thus 

 a little behind that of the other plates of the region. 



Stage II. — In a 28 mm. embryo, near the term of intra- 

 marsupial life, the post-temporal is present in the form of a 

 slender V-shaped ossification at the anterior eud of the upper 

 part of the clavicle. The clavicle is stouter than in the las 

 stage and has now the general form and features of its adult 

 state. The stem is branched and the outer branch passes 

 downward external to the muscle to the hyoid and gives 

 support to the upper part of the jugular plate. The upper 

 laminar part of the clavicle extends backward behind the 

 stem, and is attached to the transverse process of the 

 second vertebra as well as to that of the first. 



In this stage the coraco-scapular cartilage (fig. 2) still 

 forms the greater part of the shoulder-girdle and is now flat 

 behind. The coracoid region (c) is better defined than in 

 the previous stage, being slightly thicker than the remainder 

 of the cartilage, to the plane of which it now lies somewhat 

 internal. The precoracoid process {pr.p) has increased con- 

 siderably in diameter without any appreciable increase in 

 length, and is no longer a distinct process, but rather a part 

 of the coracoid. The postcoracoid process {pt.p) forms a 

 small ossified projection at the posterior border of the 



* Ivazanetf, " Ueber die Entsteluiiig des ITautpanzers bei Sunpicdfms 

 acits,'' Zool. Auz. xxx. (1906). 



