PECTORAL GIRDLE IN VERTEBRATES
SCOLIODON : PECTORAL GIRDLE
- Pectoral girdle. V-shaped structure made up of right and left halves united mid-ventrally. Each half is made up of coracoid portion, scapular portion and suprascapular portion. Pectoral girdle is embedded in lateral and ventral body wall posterior to gills in the region of heart. Pectoral girdles provide attachment to myotomes, pectoral fins and other muscles. Pectoral girdle also supports and
- Pectoral fins :- A pectoral fill is made up of basal and radial cartilages. Basal cartilages are propterygium, mesopterygium and metapterygium. Proximally these cartilages articulate with scapular and coracoid portions of pectoral girdle. From basal cartilages extend numerous radial cartilages or somactidia, each made up of 2 or 3 segments.
- Distal somactidia contain two sets of long numerous thread-like stiff and horny fin rays or ceratotrichia which support the peripheral membranous part of pectoral fin.
- Coracoid portion contains foramina for branchial artery and nerves.
FROG : PECTORAL GIRDLE
- Pectoral girdle is found embedded in the body wall in thoracic region. It is composed of two identical halves which are permanently attached with sternum.
- Each half is composed of scapular and coracoid regions.
- Scapular region consists of suprascapula and scapula. Suprascapula is a broad, flat and rectangular bone having free calcified cartilaginous margin. Scapula is also flat and contains a cup-like glenoid cavity for humerus.
- Coracoid region is made up of two bones, namely clavicle and coracoid, and two cartilages viz. epicoracoid and precoracoid.
- Pectoral girdle protects viscera and gives support to limbs. Other structures seen regarding sternum are episternum, omosternum xiphisternum and mesosternum.
VARANUS : PECTORAL GIRDLE
- Pectoral girdle of Varanus is also made up of two identical halves, firmly attached with a T-shaped interclavicle or episternum.
- Each half is composed of suprascapula, scapula, coracoid, interclavicle and clavicle.
- Suprascapula :- It is flattened, calcified and cartilaginous plate, articulating ventrally with scapula. Its dorsal margin is free and curved.
- Scapula :- It is completely ossified, flattened and unfenestrated plate, articulating with suprascapula and coracoid.
- Coracoid :- It is a flat bone partly ossified and partly cartilaginous. It contains two large fenestrae, which divide ossified region into three parts, namely anterior procoracoid, middle mesocoracoid and
posterior broad coracoid proper. Inner end of coracoid lying over fenestrae is cartilaginous and termed epicoracoid. At the posterior junction of scapula and coracoid is a cup-shaped glenoid cavity
for the head of humerus.
- Interclavicle or episternum :- T-shaped investing bone between two halves.
Clavicle :- Short, curved dermal bone, articulating with suprascapula and interclavicle.
FOWL : PECTORAL GIRDLE
- Pectoral girdle is peculiarly inverted L-shaped (7) and composed of coracoid, scapula and clavicle.
- Coracoid :- (i) It is a large, stout and rod-shaped bone. (ii) Distal end is produced into a hook-like acrocoracoid process, while proximal end is flattened to articulate with coracoid groove on the antero-Iateral border of sternum. (iii) Below acrocoracoid process, the inner surface of coracoid articulates with scapula, while outer surface contains a cup-shaped glenoid cavity for humerus head.
- Scapula :- (i) It is a sabre-like bone. (ii) Anteriorly it contains a cup-shaped depression, forming part of glenoid cavity and on inner side it has an acromian process.
- Clavicles :- (i) They fuse to form a V-shaped furcula or merry thought or wishbone. (ii) Each clavicle is a rod-shaped bone. (iii) Ventrally both clavicles unite to form interclavicle or hypocleidium.
RABBIT : PECTORAL GIRDLE
- Each half of pectoral girdle is made up of clavicle and scapula-coracoid.
- Scapula-coracoid :-
- It is a triangular replacing bone.
- The apex contains a concavity called glenoid cavity for humerus head.
- Over glenoid cavity hangs a coracoid process.
- A distinct vertical spine divides outer surface of scapula and it terminates below into an acromian process, which further gives posteriorly a metacromian process.
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