In human anatomy of the arm, the capitulum of the humerus is a smooth, rounded eminence on the lateral portion of the distal articular surface of the
humerus
The humerus (; ) is a long bone in the arm that runs from the shoulder to the elbow. It connects the scapula and the two bones of the lower arm, the radius and ulna, and consists of three sections. The humeral upper extremity consists of a roun ...
. It articulates with the cupshaped depression on the
head of the radius
The head of the radius has a cylindrical form, and on its upper surface is a shallow cup or fovea for articulation with the capitulum of the humerus. The circumference of the head is smooth; it is broad medially where it articulates with the radi ...
, and is limited to the front and lower part of the bone.
In non-human tetrapods, the name capitellum is generally used, with "capitulum" limited to the anteroventral articular facet of the rib (in archosauromorphs).
Lepidosauromorpha
Lepidosaurs
The Lepidosauria (, from Greek meaning ''scaled lizards'') is a subclass or superorder of reptiles, containing the orders Squamata and Rhynchocephalia. Squamata includes snakes, lizards, and amphisbaenians. Squamata contains over 9,000 species ...
show a distinct capitellum and
trochlea
Trochlea (Latin for pulley) is a term in anatomy. It refers to a grooved structure reminiscent of a pulley's wheel.
Related to joints
Most commonly, trochleae bear the articular surface of saddle joint, saddle and other joints:
* Trochlea of hume ...
on the centre of the ventral (anterior in upright taxa) surface of the humerus at the distal end.
Archosauromorpha
In non-avian
archosaurs
Archosauria () is a clade of diapsids, with birds and crocodilians as the only living representatives. Archosaurs are broadly classified as reptiles, in the cladistic sense of the term which includes birds. Extinct archosaurs include non-avi ...
, including crocodiles, the capitellum and the trochlea are no longer bordered by distinct etc.- and entepicondyles respectively, and the distal humerus consists two gently expanded condyles, one lateral and one medial, separated by a shallow groove and a supinator process. Romer (1976) homologizes the capitellum in Archosauromorphs with the groove separating the medial and lateral condyles.
In
bird
Birds are a group of warm-blooded vertebrates constituting the class Aves (), characterised by feathers, toothless beaked jaws, the laying of hard-shelled eggs, a high metabolic rate, a four-chambered heart, and a strong yet lightweigh ...
s, where forelimb anatomy has an
adaptation
In biology, adaptation has three related meanings. Firstly, it is the dynamic evolutionary process of natural selection that fits organisms to their environment, enhancing their evolutionary fitness. Secondly, it is a state reached by the po ...
for flight, its functional if not
ontogenetic
Ontogeny (also ontogenesis) is the origination and development of an organism (both physical and psychological, e.g., moral development), usually from the time of fertilization of the egg to adult. The term can also be used to refer to the st ...
equivalent is the dorsal condyle of the humerus.
Additional images
File:Elbow joint - deep dissection (anterior view, human cadaver).jpg, Elbow joint. Deep dissection. Anterior view.
File:Slide1bgbg.JPG, Elbow joint. Deep dissection. Posterior view.
File:Slide3bgbg.JPG, Elbow joint. Deep dissection. Posterior view.
References
* Romer, A.S. 1976 Osteology of the reptiles. University of Chicago Press, Chicago.
External links
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