The apoptosis and dysfunction of vascular smooth muscle cells in the human descending thoracic aorta is often associated with cardiovascular diseases like aortic dissection and aneurysms. Knowledge of the mechanical effects of contractile smooth muscle cells plays a crucial role in the understanding these potentially lethal conditions. Located in the medial layer, vascular smooth muscle cells are arranged in the so-called herringbone pattern. In regards to the mechanics of the aorta, the consequences of this type of anisotropy have not been fully discussed in literature so far. In this end, a novel hyperelastic constitutive law is proposed which accounts for the dispersive, transmural alignment of vascular smooth muscle cells and their characteristic length-tension behaviour. The model is calibrated with experimental data and is applied to the simulation of an aortic ring under in vivo conditions. By approximating the geometry of the aorta as a layered, thick-walled cylinder, the corresponding quasistatic, mechanical boundary value problem is solved semi-analytically. It is shown that the herringbone pattern induces shear deformation and equalises the normal stress gradients in the aortic wall. Since arterial vessels are able to actively adapt and alter the alignment and activity of smooth muscle cells, the existence of the herringbone pattern is in accordance with Fung's principle of optimal operation.