Deer antlers are bony outgrowths of the skull.  Deer antler tissue is nevertheless very different to the skull in both structure and composition.

Cell types
The growing tip of the antler is composed of various types of cells (mesenchymal, pre-chondroblasts and chondroblasts) and is covered by a layer of tissue (comprising epidermis and dermis).  The lower (non-growing) regions of the growing antler are composed of further types of cells again (chondroblasts and osteoblasts), as shown in the following diagram.

Antler composition
Mature antler is similar to compact skeletal bone in compostion, being 25% calcium and 19% phosphorus.  Organic matter contributes 39% to antler weight and water content is 8%.  

Antler has greater tensile strength but less elasticity than the human tibia.  Its resistance to impact is greater than ivory.  It is able to absorb a considerable amount of energy under impact before breaking.

Blood supply
Blood supply to the pedicles is from internal vascular supply to the frontal bones, from branches of the superficial temporal arteries.  Below the pedicle, the superficial temporal arteries give rise to large lateral coronal arteries and smaller medial coronal artiers which ascend the antler in the vascular layer of the velvet to supply blood to the velvet and bone.  Deoxygenated venal blood is returned through the antler core.  One large vein accompanies the lateral arterial arteries and one smaller vein accompanies the medial arteries, both of which evenually join the superficial temporal vein. 
Blood supply diminishes as calcification progresses.

Innervation to the antler is by the trigeminal nerve by way of supraorbital temporal branches, which are close to the lateral and medial coronal arteries.  The posterior border of the pedicle is also supplied by sensory branches of the first cervical nerves.  Upon casting, the nerves degenerate back to the pedicle and regenerate upon antler re-generation.

Deer antlers follow an annual growing cycle and are cast every year